diff --git a/2015/10/code.py b/2015/10/code.py
new file mode 100644
index 0000000..af5633f
--- /dev/null
+++ b/2015/10/code.py
@@ -0,0 +1,40 @@
+import unittest
+
+from itertools import groupby
+
+
+def say(number: str) -> str:
+    return "".join(f"{len(list(group))}{digit}" for digit, group in groupby(number))
+
+
+class TestCode(unittest.TestCase):
+    def test_say(self) -> None:
+        self.assertEqual(say(number="1"), "11")
+        self.assertEqual(say(number="11"), "21")
+        self.assertEqual(say(number="21"), "1211")
+        self.assertEqual(say(number="1211"), "111221")
+        self.assertEqual(say(number="111221"), "312211")
+
+
+class TestPuzzles(unittest.TestCase):
+    def setUp(self) -> None:
+        with open("input.txt") as f:
+            self.number = f.read().splitlines()[0]
+
+    def test_part_one(self) -> None:
+        solution = self.number
+        for _ in range(40):
+            solution = say(solution)
+        self.assertEqual(
+            len(solution),
+            492982,
+        )
+
+    def test_part_two(self) -> None:
+        solution = self.number
+        for _ in range(50):
+            solution = say(solution)
+        self.assertEqual(
+            len(solution),
+            6989950,
+        )
diff --git a/2015/10/input.txt b/2015/10/input.txt
new file mode 100644
index 0000000..067b0ee
--- /dev/null
+++ b/2015/10/input.txt
@@ -0,0 +1 @@
+1321131112