diff --git a/trees/is_valid_bst.py b/trees/is_valid_bst.py
new file mode 100644
index 0000000..ec7a1dc
--- /dev/null
+++ b/trees/is_valid_bst.py
@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
+
+
+def is_valid_bst_recursive(root):
+  
+          def is_valid(root, min_val=float(-inf), max_val=float(inf)):
+            if root is None:
+                return True
+        
+            return (min_val < root.val < max_val) and \
+                        is_valid(root.left, min_val, root.val) and \
+                        is_valid(root.right, root.val, max_val)
+        
+      return is_valid(root)
+
+
+def is_valid_bst_iterative(root):
+        
+        queue = deque()
+        queue.append((root, float(-inf), float(inf)))
+        
+        while queue:
+            node, min_val, max_val = queue.popleft()
+            if node:
+                if min_val >= node.val or node.val >= max_val:
+                    return False
+                if node.left:
+                    queue.append((node.left, min_val, node.val))
+                if node.right:
+                    queue.append((node.right, node.val, max_val))
+        
+        return True
+    
+    
+def is_valid_bst_inorder(root):
+        
+        def inorder(node):
+            if node is None:
+                return True
+            
+            inorder(node.left)
+            queue.append(node.val)
+            inorder(node.right)
+            
+        queue = []
+        inorder(root)
+        for i in range(1, len(queue)):
+            if queue[i] <= queue[i-1]:
+                return False
+            
+        return True
+