diff --git a/dungeonbattle/entities/monsters.py b/dungeonbattle/entities/monsters.py
index f7dd413..67063da 100644
--- a/dungeonbattle/entities/monsters.py
+++ b/dungeonbattle/entities/monsters.py
@@ -1,5 +1,6 @@
 from random import choice
 
+from .player import Player
 from ..interfaces import FightingEntity, Map
 
 
@@ -9,12 +10,32 @@ class Monster(FightingEntity):
         By default, a monster will move randomly where it is possible
         And if a player is close to the monster, the monster run on the player.
         """
-        # TODO If a player is close, move to the player
-        for _ in range(100):
-            if choice([self.move_up, self.move_down,
-                      self.move_left, self.move_right])():
+        target = None
+        for entity in m.entities:
+            if self.distance_squared(entity) <= 25 and \
+                    isinstance(entity, Player):
+                target = entity
                 break
 
+        if target:
+            # Move to target player
+            y, x = self.vector(target)
+            if abs(y) > abs(x):  # Move vertically
+                if y > 0:
+                    self.move_down()
+                else:
+                    self.move_up()
+            else:  # Move horizontally
+                if x > 0:
+                    self.move_right()
+                else:
+                    self.move_left()
+        else:
+            for _ in range(100):
+                if choice([self.move_up, self.move_down,
+                          self.move_left, self.move_right])():
+                    break
+
 
 class Hedgehog(Monster):
     name = "hedgehog"
diff --git a/dungeonbattle/interfaces.py b/dungeonbattle/interfaces.py
index 04ed8d1..5611795 100644
--- a/dungeonbattle/interfaces.py
+++ b/dungeonbattle/interfaces.py
@@ -1,7 +1,8 @@
 #!/usr/bin/env python
 from enum import Enum, auto
+from math import sqrt
 from random import randint
-from typing import List
+from typing import List, Tuple
 
 from dungeonbattle.display.texturepack import TexturePack
 
@@ -172,6 +173,22 @@ class Entity:
         """
         pass
 
+    def distance_squared(self, other: "Entity") -> int:
+        """
+        Get the square of the distance to another entity.
+        Useful to check distances since square root takes time.
+        """
+        return (self.y - other.y) ** 2 + (self.x - other.x) ** 2
+
+    def distance(self, other: "Entity") -> float:
+        """
+        Get the cartesian distance to another entity.
+        """
+        return sqrt(self.distance_squared(other))
+
+    def vector(self, other: "Entity") -> Tuple[int, int]:
+        return other.y - self.y, other.x - self.x
+
 
 class FightingEntity(Entity):
     maxhealth: int
diff --git a/dungeonbattle/tests/entities_test.py b/dungeonbattle/tests/entities_test.py
index adca2ec..3d61812 100644
--- a/dungeonbattle/tests/entities_test.py
+++ b/dungeonbattle/tests/entities_test.py
@@ -23,6 +23,11 @@ class TestEntities(unittest.TestCase):
         self.assertEqual(entity.x, 64)
         self.assertIsNone(entity.act(self.map))
 
+        other_entity = Entity()
+        other_entity.move(45, 68)
+        self.assertEqual(entity.distance_squared(other_entity), 25)
+        self.assertEqual(entity.distance(other_entity), 5)
+
     def test_fighting_entities(self) -> None:
         """
         Test some random stuff with fighting entities.