diff --git a/Cargo.lock b/Cargo.lock
index 26c2a1d..0efd066 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -762,6 +762,10 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "mutable-references"
+version = "0.1.0"
+
 [[package]]
 name = "mutable-variables"
 version = "0.1.0"
diff --git a/challenges/challenges.json b/challenges/challenges.json
index ce1e611..c6dc8d3 100644
--- a/challenges/challenges.json
+++ b/challenges/challenges.json
@@ -227,6 +227,18 @@
     "created_at": "2024-06-13T00:00:00Z",
     "updated_at": "2024-06-13T00:00:00Z"
   },
+  {
+    "id": 35,
+    "title": "Mutable References",
+    "slug": "mutable-references",
+    "short_description": "Implement Rust's ownership model with mutable references.",
+    "language": "RUST",
+    "difficulty": "BEGINNER",
+    "track": "RUST_BASICS",
+    "tags": ["ownership", "borrowing", "mutable references"],
+    "created_at": "2024-06-13T00:00:00Z",
+    "updated_at": "2024-06-13T00:00:00Z"
+  },
   {
     "id": 2,
     "title": "Character counting string",
diff --git a/challenges/mutable-references/Cargo.toml b/challenges/mutable-references/Cargo.toml
new file mode 100644
index 0000000..54db61d
--- /dev/null
+++ b/challenges/mutable-references/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "mutable-references"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/challenges/mutable-references/description.md b/challenges/mutable-references/description.md
new file mode 100644
index 0000000..4eab4c4
--- /dev/null
+++ b/challenges/mutable-references/description.md
@@ -0,0 +1,40 @@
+Rust's ownership model ensures memory safety without needing a garbage collector. In the previous challenge, you learned about **immutable references**. Now, let's dive into **mutable references**.
+
+## Mutable References
+
+**Mutable references** allow you to **modify** the value you are **borrowing**. **You can only have one mutable reference to a particular piece of data in a particular scope.** This prevents data races at compile time.
+
+### Example
+
+```rust
+fn main() {
+    let mut s = String::from("hello");
+
+    change(&mut s); // borrow s as mutable
+    println!("{}", s);
+}
+
+fn change(some_string: &mut String) {
+    some_string.push_str(", world");
+}
+```
+
+## Challenge
+
+Create a function `append_suffix` that takes a mutable reference to a `String` and appends a given suffix to it.
+
+## Requirements
+
+- The `append_suffix` function should take **a mutable reference** to the input `String` and append the given suffix to it.
+
+## Example
+
+```rust
+let mut s2 = String::from("hello");
+append_suffix(&mut s2, " world");
+assert_eq!(s2, "hello world");
+```
+
+## Hints
+
+- The `String` type in Rust has methods like `push_str` which can be useful for modifying strings.
diff --git a/challenges/mutable-references/src/lib.rs b/challenges/mutable-references/src/lib.rs
new file mode 100644
index 0000000..c9ac390
--- /dev/null
+++ b/challenges/mutable-references/src/lib.rs
@@ -0,0 +1,3 @@
+pub fn append_suffix(s: &mut String, suffix: &str) {
+    s.push_str(suffix);
+}
diff --git a/challenges/mutable-references/src/starter.rs b/challenges/mutable-references/src/starter.rs
new file mode 100644
index 0000000..47a732d
--- /dev/null
+++ b/challenges/mutable-references/src/starter.rs
@@ -0,0 +1,3 @@
+pub fn append_suffix(s: &mut String, suffix: &str) {
+    // Your code here...
+}
diff --git a/challenges/mutable-references/tests/tests.rs b/challenges/mutable-references/tests/tests.rs
new file mode 100644
index 0000000..592c4be
--- /dev/null
+++ b/challenges/mutable-references/tests/tests.rs
@@ -0,0 +1,20 @@
+#[cfg(test)]
+mod tests {
+    use mutable_references::append_suffix;
+
+    #[test]
+    fn test_append_suffix() {
+        let mut s = String::from("hello");
+        append_suffix(&mut s, " world");
+        assert_eq!(s, "hello world");
+
+        append_suffix(&mut s, "!");
+        assert_eq!(s, "hello world!");
+
+        append_suffix(&mut s, "??");
+        assert_eq!(s, "hello world!??");
+
+        append_suffix(&mut s, " I love Rust!");
+        assert_eq!(s, "hello world!?? I love Rust!");
+    }
+}