diff --git a/1_concepts/src/main.rs b/1_concepts/src/main.rs
index 4722cdb..49de845 100644
--- a/1_concepts/src/main.rs
+++ b/1_concepts/src/main.rs
@@ -1,3 +1,238 @@
+use crate::list::CustomLinkedList;
+use std::collections::LinkedList;
+
 fn main() {
-    println!("Implement me!");
+    let mut playlist_custom: CustomLinkedList<String> = CustomLinkedList::new();
+    let mut playlist_std: LinkedList<String> = LinkedList::new();
+
+    playlist_custom.push_back("Song 1".to_owned());
+    playlist_std.push_back("Song 1".to_owned());
+    playlist_custom.push_back("Song 2".to_owned());
+    playlist_std.push_back("Song 2".to_owned());
+    playlist_custom.push_front("Intro".to_owned());
+    playlist_std.push_front("Intro".to_owned());
+
+    for song in playlist_custom.iter() {
+        println!("Playing custom: {}", song);
+    }
+    for song in playlist_std.iter() {
+        println!("Playing std: {}", song);
+    }
+
+    playlist_custom.pop_back();
+    playlist_std.pop_back();
+
+    playlist_custom.pop_front();
+    playlist_std.pop_front();
+
+    for song in playlist_custom.iter() {
+        println!("Playing custom: {}", song);
+    }
+    for song in playlist_std.iter() {
+        println!("Playing std: {}", song);
+    }
+}
+
+pub mod list {
+    use std::{
+        sync::{Arc, Mutex, Weak},
+    };
+
+    #[derive(Clone)]
+    pub struct CustomLinkedList<T: Clone> {
+        inner: Arc<Mutex<InnerLinkedList<T>>>,
+    }
+    impl<T: Clone> CustomLinkedList<T> {
+        pub fn new() -> Self {
+            Self {
+                inner: Arc::new(Mutex::new(InnerLinkedList::new())),
+            }
+        }
+
+        pub fn push_back(&mut self, data: T) {
+            self.inner.lock().unwrap().push_back(data);
+        }
+
+        pub fn pop_back(&mut self) {
+            self.inner.lock().unwrap().pop_back();
+        }
+
+        pub fn pop_front(&mut self) {
+            self.inner.lock().unwrap().pop_front();
+        }
+
+        pub fn push_front(&mut self, data: T) {
+            self.inner.lock().unwrap().push_front(data);
+        }
+
+        pub fn iter(&self) -> Iter<T> {
+            self.inner.lock().unwrap().iter()
+        }
+    }
+
+    #[derive(Debug)]
+    struct InnerLinkedList<T> {
+        head: Option<Arc<Mutex<Link<T>>>>,
+        tail: Option<Arc<Mutex<Link<T>>>>,
+    }
+    impl<T: Clone> InnerLinkedList<T> {
+        fn new() -> Self {
+            Self {
+                head: None,
+                tail: None,
+            }
+        }
+
+        fn push_back(&mut self, data: T) {
+            let link = Arc::new(Mutex::new(Link::new(data)));
+
+            if let Some(tail) = &mut self.tail {
+                tail.lock().unwrap().next = Some(Arc::clone(&link));
+                link.lock().unwrap().prev = Some(Arc::downgrade(&tail));
+                self.tail = Some(Arc::clone(&link));
+            } else {
+                self.head = Some(Arc::clone(&link));
+                self.tail = Some(Arc::clone(&link));
+            }
+        }
+
+        fn push_front(&mut self, data: T) {
+            let link = Arc::new(Mutex::new(Link::new(data)));
+
+            if let Some(head) = &mut self.head {
+                head.lock().unwrap().prev = Some(Arc::downgrade(&link));
+                link.lock().unwrap().next = Some(Arc::clone(&head));
+                self.head = Some(Arc::clone(&link));
+            } else {
+                self.head = Some(Arc::clone(&link));
+                self.tail = Some(Arc::clone(&link));
+            }
+        }
+
+        fn pop_back(&mut self) -> Option<T> {
+            self.tail.take().map(|tail| {
+                let mut tail = tail.lock().unwrap();
+                let data = tail.data.clone();
+
+                if let Some(prev) = tail.prev.take() {
+                    let prev = prev.upgrade().unwrap();
+                    prev.lock().unwrap().next = None;
+                    self.tail = Some(prev);
+                } else {
+                    self.head = None;
+                    self.tail = None;
+                }
+
+                data
+            })
+        }
+
+        fn pop_front(&mut self) -> Option<T> {
+            self.head.take().map(|head| {
+                let mut head = head.lock().unwrap();
+                let data = head.data.clone();
+
+                if let Some(next) = head.next.take() {
+                    next.lock().unwrap().next = None;
+                    self.head = Some(next);
+                } else {
+                    self.head = None;
+                    self.tail = None;
+                }
+
+                data
+            })
+        }
+
+        fn iter(&self) -> Iter<T> {
+            let mut vec = Vec::new();
+            let mut current = self.head.clone();
+            while let Some(link) = current {
+                let link_guard = link.lock().unwrap();
+                vec.push(link_guard.data.clone());
+                current = link_guard.next.clone();
+            }
+            Iter {
+                inner: vec.into_iter(),
+            }
+        }
+    }
+    impl<T> Iterator for Iter<T> {
+        type Item = T;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            self.inner.next()
+        }
+    }
+
+    pub struct Iter<T> {
+        inner: std::vec::IntoIter<T>,
+    }
+
+    #[derive(Debug)]
+    struct Link<T> {
+        prev: Option<Weak<Mutex<Link<T>>>>,
+        next: Option<Arc<Mutex<Link<T>>>>,
+        data: T,
+    }
+    impl<T> Link<T> {
+        fn new(data: T) -> Self {
+            Link {
+                prev: None,
+                data,
+                next: None,
+            }
+        }
+    }
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+        use std::collections::LinkedList;
+
+        #[test]
+        fn test_correctness() {
+            let mut custom = CustomLinkedList::new();
+            let mut std = LinkedList::new();
+
+            custom.push_back("Song 1".to_string());
+            std.push_back("Song 1".to_string());
+            custom.push_back("Song 2".to_string());
+            std.push_back("Song 2".to_string());
+            custom.push_front("Intro".to_string());
+            std.push_front("Intro".to_string());
+
+            let custom_vec: Vec<_> = custom.iter().collect();
+            let std_vec: Vec<_> = std.iter().cloned().collect();
+            assert_eq!(custom_vec, std_vec);
+
+            custom.pop_back();
+            std.pop_back();
+            let custom_vec: Vec<_> = custom.iter().collect();
+            let std_vec: Vec<_> = std.iter().cloned().collect();
+            assert_eq!(custom_vec, std_vec);
+
+            custom.pop_front();
+            std.pop_front();
+            let custom_vec: Vec<_> = custom.iter().collect();
+            let std_vec: Vec<_> = std.iter().cloned().collect();
+            assert_eq!(custom_vec, std_vec);
+        }
+
+        #[test]
+        fn test_multi_threaded() {
+            let mut list = CustomLinkedList::new();
+            list.push_back(1);
+            list.push_back(2);
+
+            let handle = std::thread::spawn(move || {
+                list.push_back(3);
+                list.push_front(0);
+                list
+            });
+
+            let list = handle.join().unwrap();
+            let vec: Vec<_> = list.iter().collect();
+            assert_eq!(vec, vec![0, 1, 2, 3]);
+        }
+    }
 }
diff --git a/README.md b/README.md
index 21e941e..e795ea3 100644
--- a/README.md
+++ b/README.md
@@ -70,7 +70,7 @@ This project represents a hard-way step-by-step [Rust] learning course from lang
 Each step must be performed as a separate [PR (pull request)][PR] with an appropriate name and check-marked here in the README's schedule after completion. Each step is a [Cargo workspace member][13], so you can run/test it from the project root (i.e. `cargo run -p step_1_8`). __Consider using [rustfmt] and [Clippy] when you're writing [Rust] code.__
 
 - [x] [0. Become familiar with Rust basics][Step 0] (3 days)
-- [ ] [1. Concepts][Step 1] (2 days, after all sub-steps)
+- [x] [1. Concepts][Step 1] (2 days, after all sub-steps)
     - [ ] [1.1. Default values, cloning and copying][Step 1.1] (1 day)
     - [ ] [1.2. Boxing and pinning][Step 1.2] (1 day)
     - [ ] [1.3. Shared ownership and interior mutability][Step 1.3] (1 day)