diff --git a/src/ZugferdDocumentBuilder.php b/src/ZugferdDocumentBuilder.php
index 0846c2e..d4f6be0 100644
--- a/src/ZugferdDocumentBuilder.php
+++ b/src/ZugferdDocumentBuilder.php
@@ -412,6 +412,19 @@ public function setDocumentSeller(string $name, ?string $id = null, ?string $des
         return $this;
     }
 
+    /**
+     * Add an id to the document seller
+     *
+     * @param  string|null $id          __BT-29, From BASIC WL__ An identifier of the seller. In many systems, seller identification is key information. Multiple seller IDs can be assigned or specified. They can be differentiated by using different identification schemes. If no scheme is given, it should be known to the buyer and seller, e.g. a previously exchanged, buyer-assigned identifier of the seller
+     * @return ZugferdDocumentBuilder
+     */
+    public function addDocumentSellerId(string $id): ZugferdDocumentBuilder
+    {
+        $sellerTradeParty = $this->getObjectHelper()->tryCallAndReturn($this->headerTradeAgreement, "getSellerTradeParty");
+        $this->getObjectHelper()->tryCall($sellerTradeParty, "addToID", $this->getObjectHelper()->getIdType($id));
+        return $this;
+    }
+
     /**
      * Add a global id for the seller
      *
@@ -556,6 +569,19 @@ public function setDocumentBuyer(string $name, ?string $id = null, ?string $desc
         return $this;
     }
 
+    /**
+     * Add an id to the document buyer
+     *
+     * @param  string|null $id          __BT-46, From BASIC WL__ An identifier of the buyer. In many systems, buyer identification is key information. Multiple buyer IDs can be assigned or specified. They can be differentiated by using different identification schemes. If no scheme is given, it should be known to the buyer and buyer, e.g. a previously exchanged, seller-assigned identifier of the buyer
+     * @return ZugferdDocumentBuilder
+     */
+    public function addDocumentBuyerId(string $id): ZugferdDocumentBuilder
+    {
+        $buyerTradeParty = $this->getObjectHelper()->tryCallAndReturn($this->headerTradeAgreement, "getBuyerTradeParty");
+        $this->getObjectHelper()->tryCall($buyerTradeParty, "addToID", $this->getObjectHelper()->getIdType($id));
+        return $this;
+    }
+
     /**
      * Add a global id for the buyer
      *
diff --git a/tests/testcases/BuilderEn16931Test.php b/tests/testcases/BuilderEn16931Test.php
index a804728..6633e1b 100644
--- a/tests/testcases/BuilderEn16931Test.php
+++ b/tests/testcases/BuilderEn16931Test.php
@@ -186,6 +186,21 @@ public function testSetDocumentSeller(): void
         $this->assertXPathNotExists('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:Name');
     }
 
+    /**
+     * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentSellerId
+     */
+    public function testAddDocumentSellerId(): void
+    {
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 0, "5499103");
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 1);
+
+        (self::$document)->addDocumentSellerId('5499104');
+
+        $this->disableRenderXmlContent();
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 0, "5499103");
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 1, "5499104");
+    }
+
     /**
      * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentSellerGlobalId
      */
@@ -334,6 +349,21 @@ public function testSetDocumentBuyer(): void
         $this->assertXPathValue('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:Name', "Kunden AG Mitte");
     }
 
+    /**
+     * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentBuyerId
+     */
+    public function testAddDocumentBuyerId(): void
+    {
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 0, "549910");
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 1);
+
+        (self::$document)->addDocumentBuyerId('549911');
+
+        $this->disableRenderXmlContent();
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 0, "549910");
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 1, "549911");
+    }
+
     /**
      * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentBuyerGlobalId
      */
diff --git a/tests/testcases/BuilderExtendedTest.php b/tests/testcases/BuilderExtendedTest.php
index e9e9380..fd335e2 100644
--- a/tests/testcases/BuilderExtendedTest.php
+++ b/tests/testcases/BuilderExtendedTest.php
@@ -175,6 +175,21 @@ public function testSetDocumentSeller(): void
         $this->assertXPathValue('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:Name', "Lieferant GmbH");
     }
 
+    /**
+     * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentSellerId
+     */
+    public function testAddDocumentSellerId(): void
+    {
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 0, "549910");
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 1);
+
+        (self::$document)->addDocumentSellerId('549911');
+
+        $this->disableRenderXmlContent();
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 0, "549910");
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 1, "549911");
+    }
+
     /**
      * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentSellerGlobalId
      */
@@ -328,6 +343,21 @@ public function testSetDocumentBuyer(): void
         $this->assertXPathValue('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:Name', "Kunden AG Mitte");
     }
 
+    /**
+     * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentBuyerId
+     */
+    public function testAddDocumentBuyerId(): void
+    {
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 0, "549910");
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 1);
+
+        (self::$document)->addDocumentBuyerId('549911');
+
+        $this->disableRenderXmlContent();
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 0, "549910");
+        $this->assertXPathValueWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 1, "549911");
+    }
+
     /**
      * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentBuyerGlobalId
      */
diff --git a/tests/testcases/BuilderMinimumTest.php b/tests/testcases/BuilderMinimumTest.php
index a04c063..ee20254 100644
--- a/tests/testcases/BuilderMinimumTest.php
+++ b/tests/testcases/BuilderMinimumTest.php
@@ -189,6 +189,21 @@ public function testSetDocumentSeller(): void
         $this->assertXPathNotExists('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:Name');
     }
 
+    /**
+     * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentSellerId
+     */
+    public function testAddDocumentSellerId(): void
+    {
+        $this->assertXPathNotExists('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 0);
+        $this->assertXPathNotExists('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 1);
+
+        (self::$document)->addDocumentSellerId('549911');
+
+        $this->disableRenderXmlContent();
+        $this->assertXPathNotExists('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 0);
+        $this->assertXPathNotExists('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:ID', 1);
+    }
+
     /**
      * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentSellerGlobalId
      */
@@ -337,6 +352,21 @@ public function testSetDocumentBuyer(): void
         $this->assertXPathValue('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:Name', "Kunden AG Mitte");
     }
 
+    /**
+     * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentBuyerId
+     */
+    public function testAddDocumentBuyerId(): void
+    {
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 0);
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 1);
+
+        (self::$document)->addDocumentBuyerId('549911');
+
+        $this->disableRenderXmlContent();
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 0);
+        $this->assertXPathNotExistsWithIndex('/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:BuyerTradeParty/ram:ID', 1);
+    }
+
     /**
      * @covers \horstoeko\zugferd\ZugferdDocumentBuilder::addDocumentBuyerGlobalId
      */