diff --git a/README.md b/README.md
index f07db941..1c92b7df 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,9 @@ Note that this repository is currently under development, additional classes and
 
 ## Getting Started
 
+The Cloudflare PHP SDK requires a HTTP Client adapter to works with.
+You can either use the Guzzle adapter shipped with the library and by installing Guzzle (`composer require guzzlehttp/guzzle:^7.0`), or implement your own Adapter by implementing the `Cloudflare\API\Adapter\Adapter` interface.
+
 ```php
 $key     = new Cloudflare\API\Auth\APIKey('user@example.com', 'apiKey');
 $adapter = new Cloudflare\API\Adapter\Guzzle($key);
diff --git a/composer.json b/composer.json
index 81112ad0..3c68973e 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,6 @@
   "description": "PHP binding for v4 of the Cloudflare Client API.",
   "type": "library",
   "require": {
-    "guzzlehttp/guzzle": "^7.0.1",
     "php": ">=7.2.5",
     "psr/http-message": "~1.0",
     "ext-json": "*"
@@ -11,7 +10,8 @@
   "require-dev": {
     "phpunit/phpunit": "^5.7",
     "phpmd/phpmd" : "@stable",
-    "friendsofphp/php-cs-fixer": "^2.6"
+    "friendsofphp/php-cs-fixer": "^2.6",
+    "guzzlehttp/guzzle": "^7.0.1"
   },
   "license": "BSD-3-Clause",
   "authors": [
diff --git a/composer.lock b/composer.lock
index 633000df..3e7fc492 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,197 +4,8 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "dfd011c55474ffaab84b7a0a6d164049",
+    "content-hash": "e086064ace1bbe4b29e3c6c7d405cb19",
     "packages": [
-        {
-            "name": "guzzlehttp/guzzle",
-            "version": "6.5.2",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/guzzle/guzzle.git",
-                "reference": "43ece0e75098b7ecd8d13918293029e555a50f82"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/guzzle/guzzle/zipball/43ece0e75098b7ecd8d13918293029e555a50f82",
-                "reference": "43ece0e75098b7ecd8d13918293029e555a50f82",
-                "shasum": ""
-            },
-            "require": {
-                "ext-json": "*",
-                "guzzlehttp/promises": "^1.0",
-                "guzzlehttp/psr7": "^1.6.1",
-                "php": ">=5.5"
-            },
-            "require-dev": {
-                "ext-curl": "*",
-                "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.4 || ^7.0",
-                "psr/log": "^1.1"
-            },
-            "suggest": {
-                "ext-intl": "Required for Internationalized Domain Name (IDN) support",
-                "psr/log": "Required for using the Log middleware"
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "6.5-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "GuzzleHttp\\": "src/"
-                },
-                "files": [
-                    "src/functions_include.php"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Michael Dowling",
-                    "email": "mtdowling@gmail.com",
-                    "homepage": "https://github.com/mtdowling"
-                }
-            ],
-            "description": "Guzzle is a PHP HTTP client library",
-            "homepage": "http://guzzlephp.org/",
-            "keywords": [
-                "client",
-                "curl",
-                "framework",
-                "http",
-                "http client",
-                "rest",
-                "web service"
-            ],
-            "time": "2019-12-23T11:57:10+00:00"
-        },
-        {
-            "name": "guzzlehttp/promises",
-            "version": "v1.3.1",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/guzzle/promises.git",
-                "reference": "a59da6cf61d80060647ff4d3eb2c03a2bc694646"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/guzzle/promises/zipball/a59da6cf61d80060647ff4d3eb2c03a2bc694646",
-                "reference": "a59da6cf61d80060647ff4d3eb2c03a2bc694646",
-                "shasum": ""
-            },
-            "require": {
-                "php": ">=5.5.0"
-            },
-            "require-dev": {
-                "phpunit/phpunit": "^4.0"
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "1.4-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "GuzzleHttp\\Promise\\": "src/"
-                },
-                "files": [
-                    "src/functions_include.php"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Michael Dowling",
-                    "email": "mtdowling@gmail.com",
-                    "homepage": "https://github.com/mtdowling"
-                }
-            ],
-            "description": "Guzzle promises library",
-            "keywords": [
-                "promise"
-            ],
-            "time": "2016-12-20T10:07:11+00:00"
-        },
-        {
-            "name": "guzzlehttp/psr7",
-            "version": "1.6.1",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/guzzle/psr7.git",
-                "reference": "239400de7a173fe9901b9ac7c06497751f00727a"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/guzzle/psr7/zipball/239400de7a173fe9901b9ac7c06497751f00727a",
-                "reference": "239400de7a173fe9901b9ac7c06497751f00727a",
-                "shasum": ""
-            },
-            "require": {
-                "php": ">=5.4.0",
-                "psr/http-message": "~1.0",
-                "ralouphie/getallheaders": "^2.0.5 || ^3.0.0"
-            },
-            "provide": {
-                "psr/http-message-implementation": "1.0"
-            },
-            "require-dev": {
-                "ext-zlib": "*",
-                "phpunit/phpunit": "~4.8.36 || ^5.7.27 || ^6.5.8"
-            },
-            "suggest": {
-                "zendframework/zend-httphandlerrunner": "Emit PSR-7 responses"
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "1.6-dev"
-                }
-            },
-            "autoload": {
-                "psr-4": {
-                    "GuzzleHttp\\Psr7\\": "src/"
-                },
-                "files": [
-                    "src/functions_include.php"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Michael Dowling",
-                    "email": "mtdowling@gmail.com",
-                    "homepage": "https://github.com/mtdowling"
-                },
-                {
-                    "name": "Tobias Schultze",
-                    "homepage": "https://github.com/Tobion"
-                }
-            ],
-            "description": "PSR-7 message implementation that also provides common utility methods",
-            "keywords": [
-                "http",
-                "message",
-                "psr-7",
-                "request",
-                "response",
-                "stream",
-                "uri",
-                "url"
-            ],
-            "time": "2019-07-01T23:21:34+00:00"
-        },
         {
             "name": "psr/http-message",
             "version": "1.0.1",
@@ -244,46 +55,6 @@
                 "response"
             ],
             "time": "2016-08-06T14:39:51+00:00"
-        },
-        {
-            "name": "ralouphie/getallheaders",
-            "version": "3.0.3",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/ralouphie/getallheaders.git",
-                "reference": "120b605dfeb996808c31b6477290a714d356e822"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/ralouphie/getallheaders/zipball/120b605dfeb996808c31b6477290a714d356e822",
-                "reference": "120b605dfeb996808c31b6477290a714d356e822",
-                "shasum": ""
-            },
-            "require": {
-                "php": ">=5.6"
-            },
-            "require-dev": {
-                "php-coveralls/php-coveralls": "^2.1",
-                "phpunit/phpunit": "^5 || ^6.5"
-            },
-            "type": "library",
-            "autoload": {
-                "files": [
-                    "src/getallheaders.php"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Ralph Khattar",
-                    "email": "ralph.khattar@gmail.com"
-                }
-            ],
-            "description": "A polyfill for getallheaders.",
-            "time": "2019-03-08T08:55:37+00:00"
         }
     ],
     "packages-dev": [
@@ -663,6 +434,230 @@
             "description": "A tool to automatically fix PHP code style",
             "time": "2019-11-25T22:10:32+00:00"
         },
+        {
+            "name": "guzzlehttp/guzzle",
+            "version": "7.1.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/guzzle/guzzle.git",
+                "reference": "7427d6f99df41cc01f33cd59832f721c150ffdf3"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/guzzle/guzzle/zipball/7427d6f99df41cc01f33cd59832f721c150ffdf3",
+                "reference": "7427d6f99df41cc01f33cd59832f721c150ffdf3",
+                "shasum": ""
+            },
+            "require": {
+                "ext-json": "*",
+                "guzzlehttp/promises": "^1.0",
+                "guzzlehttp/psr7": "^1.6.1",
+                "php": "^7.2.5",
+                "psr/http-client": "^1.0"
+            },
+            "provide": {
+                "psr/http-client-implementation": "1.0"
+            },
+            "require-dev": {
+                "ext-curl": "*",
+                "php-http/client-integration-tests": "dev-phpunit8",
+                "phpunit/phpunit": "^8.5.5",
+                "psr/log": "^1.1"
+            },
+            "suggest": {
+                "ext-curl": "Required for CURL handler support",
+                "ext-intl": "Required for Internationalized Domain Name (IDN) support",
+                "psr/log": "Required for using the Log middleware"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "7.1-dev"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "src/functions_include.php"
+                ],
+                "psr-4": {
+                    "GuzzleHttp\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Michael Dowling",
+                    "email": "mtdowling@gmail.com",
+                    "homepage": "https://github.com/mtdowling"
+                },
+                {
+                    "name": "Márk Sági-Kazár",
+                    "email": "mark.sagikazar@gmail.com",
+                    "homepage": "https://sagikazarmark.hu"
+                }
+            ],
+            "description": "Guzzle is a PHP HTTP client library",
+            "homepage": "http://guzzlephp.org/",
+            "keywords": [
+                "client",
+                "curl",
+                "framework",
+                "http",
+                "http client",
+                "psr-18",
+                "psr-7",
+                "rest",
+                "web service"
+            ],
+            "support": {
+                "issues": "https://github.com/guzzle/guzzle/issues",
+                "source": "https://github.com/guzzle/guzzle/tree/7.1.1"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/GrahamCampbell",
+                    "type": "github"
+                },
+                {
+                    "url": "https://github.com/Nyholm",
+                    "type": "github"
+                },
+                {
+                    "url": "https://github.com/alexeyshockov",
+                    "type": "github"
+                },
+                {
+                    "url": "https://github.com/gmponos",
+                    "type": "github"
+                }
+            ],
+            "time": "2020-09-30T08:51:17+00:00"
+        },
+        {
+            "name": "guzzlehttp/promises",
+            "version": "v1.3.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/guzzle/promises.git",
+                "reference": "a59da6cf61d80060647ff4d3eb2c03a2bc694646"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/guzzle/promises/zipball/a59da6cf61d80060647ff4d3eb2c03a2bc694646",
+                "reference": "a59da6cf61d80060647ff4d3eb2c03a2bc694646",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.5.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.4-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "GuzzleHttp\\Promise\\": "src/"
+                },
+                "files": [
+                    "src/functions_include.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Michael Dowling",
+                    "email": "mtdowling@gmail.com",
+                    "homepage": "https://github.com/mtdowling"
+                }
+            ],
+            "description": "Guzzle promises library",
+            "keywords": [
+                "promise"
+            ],
+            "time": "2016-12-20T10:07:11+00:00"
+        },
+        {
+            "name": "guzzlehttp/psr7",
+            "version": "1.6.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/guzzle/psr7.git",
+                "reference": "239400de7a173fe9901b9ac7c06497751f00727a"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/guzzle/psr7/zipball/239400de7a173fe9901b9ac7c06497751f00727a",
+                "reference": "239400de7a173fe9901b9ac7c06497751f00727a",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.4.0",
+                "psr/http-message": "~1.0",
+                "ralouphie/getallheaders": "^2.0.5 || ^3.0.0"
+            },
+            "provide": {
+                "psr/http-message-implementation": "1.0"
+            },
+            "require-dev": {
+                "ext-zlib": "*",
+                "phpunit/phpunit": "~4.8.36 || ^5.7.27 || ^6.5.8"
+            },
+            "suggest": {
+                "zendframework/zend-httphandlerrunner": "Emit PSR-7 responses"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.6-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "GuzzleHttp\\Psr7\\": "src/"
+                },
+                "files": [
+                    "src/functions_include.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Michael Dowling",
+                    "email": "mtdowling@gmail.com",
+                    "homepage": "https://github.com/mtdowling"
+                },
+                {
+                    "name": "Tobias Schultze",
+                    "homepage": "https://github.com/Tobion"
+                }
+            ],
+            "description": "PSR-7 message implementation that also provides common utility methods",
+            "keywords": [
+                "http",
+                "message",
+                "psr-7",
+                "request",
+                "response",
+                "stream",
+                "uri",
+                "url"
+            ],
+            "time": "2019-07-01T23:21:34+00:00"
+        },
         {
             "name": "myclabs/deep-copy",
             "version": "1.7.0",
@@ -1571,6 +1566,58 @@
             ],
             "time": "2017-02-14T16:28:37+00:00"
         },
+        {
+            "name": "psr/http-client",
+            "version": "1.0.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/http-client.git",
+                "reference": "2dfb5f6c5eff0e91e20e913f8c5452ed95b86621"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-fig/http-client/zipball/2dfb5f6c5eff0e91e20e913f8c5452ed95b86621",
+                "reference": "2dfb5f6c5eff0e91e20e913f8c5452ed95b86621",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.0 || ^8.0",
+                "psr/http-message": "^1.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.0.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psr\\Http\\Client\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for HTTP clients",
+            "homepage": "https://github.com/php-fig/http-client",
+            "keywords": [
+                "http",
+                "http-client",
+                "psr",
+                "psr-18"
+            ],
+            "support": {
+                "source": "https://github.com/php-fig/http-client/tree/master"
+            },
+            "time": "2020-06-29T06:28:15+00:00"
+        },
         {
             "name": "psr/log",
             "version": "1.1.2",
@@ -1618,6 +1665,46 @@
             ],
             "time": "2019-11-01T11:05:21+00:00"
         },
+        {
+            "name": "ralouphie/getallheaders",
+            "version": "3.0.3",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/ralouphie/getallheaders.git",
+                "reference": "120b605dfeb996808c31b6477290a714d356e822"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/ralouphie/getallheaders/zipball/120b605dfeb996808c31b6477290a714d356e822",
+                "reference": "120b605dfeb996808c31b6477290a714d356e822",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.6"
+            },
+            "require-dev": {
+                "php-coveralls/php-coveralls": "^2.1",
+                "phpunit/phpunit": "^5 || ^6.5"
+            },
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "src/getallheaders.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Ralph Khattar",
+                    "email": "ralph.khattar@gmail.com"
+                }
+            ],
+            "description": "A polyfill for getallheaders.",
+            "time": "2019-03-08T08:55:37+00:00"
+        },
         {
             "name": "sebastian/code-unit-reverse-lookup",
             "version": "1.0.1",
@@ -3049,12 +3136,15 @@
     ],
     "aliases": [],
     "minimum-stability": "stable",
-    "stability-flags": [],
+    "stability-flags": {
+        "phpmd/phpmd": 0
+    },
     "prefer-stable": false,
     "prefer-lowest": false,
     "platform": {
-        "php": ">=7.0.0",
+        "php": ">=7.2.5",
         "ext-json": "*"
     },
-    "platform-dev": []
+    "platform-dev": [],
+    "plugin-api-version": "2.2.0"
 }
diff --git a/src/Adapter/Guzzle.php b/src/Adapter/Guzzle.php
index 71e7dd75..34d02f31 100644
--- a/src/Adapter/Guzzle.php
+++ b/src/Adapter/Guzzle.php
@@ -16,6 +16,10 @@ class Guzzle implements Adapter
      */
     public function __construct(Auth $auth, string $baseURI = null)
     {
+        if (false === class_exists(Client::class)) {
+            throw new \RuntimeException('The Guzzle adapter requires to have Guzzle installed, you can install it by running "composer require guzzlehttp/guzzle:^7.0".');
+        }
+
         if ($baseURI === null) {
             $baseURI = 'https://api.cloudflare.com/client/v4/';
         }