diff --git a/CombinationSum.java b/CombinationSum.java
new file mode 100644
index 00000000..3ce34791
--- /dev/null
+++ b/CombinationSum.java
@@ -0,0 +1,28 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class CombinationSum {
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+        List<List<Integer>> result = new ArrayList<>();
+        List<Integer> set = new ArrayList<>();
+        helper(candidates, target, 0, result, set);
+        return result;
+    }
+
+    private void helper(int[] candidates, int target, int idx, List<List<Integer>> result,  List<Integer> set){
+        //base
+        if(idx==candidates.length || target < 0) return;
+        if(target==0){
+            result.add( new ArrayList<>(set));
+            return;
+        }
+        //logic
+        //choose
+        set.add(candidates[idx]);
+        helper(candidates, target-candidates[idx], idx, result, set);
+        //backtracking
+        set.remove(set.size()-1);
+        //no choose
+        helper(candidates, target, idx+1, result, set);
+    }
+}