diff --git a/src/display.rs b/src/display.rs
index 60d4653..9ae1926 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -36,7 +36,7 @@ pub fn init_display(bus: I2c<'static, embassy_rp::peripherals::I2C0, embassy_rp:
 /// Temp function which updates the display with currently pressed keys
 pub fn update_display(
     display: &mut Option<Display>,
-    pressed_keys: &[(usize, usize, crate::keymap::KeyCode)],
+    pressed_keys: &[(usize, usize, crate::keymap::Action)],
 ) -> Option<()> {
     if let Some(display) = display {
         display.clear(BinaryColor::Off).ok()?;
@@ -54,7 +54,7 @@ pub fn update_display(
             let mut y_pos = 0;
             for (row_idx, col_idx, keycode) in pressed_keys.iter().take(3) {
                 let mut msg = heapless::String::<32>::new();
-                write!(&mut msg, "R{}C{}: 0x{:02X}", row_idx, col_idx, keycode.as_u8()).ok();
+                write!(&mut msg, "R{}C{}: 0x{:?}", row_idx, col_idx, keycode).ok();
     
                 Text::with_baseline(&msg, Point::new(0, y_pos), text_style, Baseline::Top)
                     .draw(display)
diff --git a/src/keymap.rs b/src/keymap.rs
index 37eb94b..69a79f5 100644
--- a/src/keymap.rs
+++ b/src/keymap.rs
@@ -2,11 +2,27 @@
 /// Reference: https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf
 /// Section 10: Keyboard/Keypad Page (0x07)
 
-#[allow(dead_code)]
+static N_LAYERS: usize = 4;
+static COLS: usize = 12;
+static ROWS: usize = 4;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Action {
+    Key(HidKey), // normal key press
+    Layer(LayerOperation), // layer modifier key press
+    None, // do nothing
+    Trans, // fall back to the default keymap
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum LayerOperation {
+    MO(usize) // momentary (hold to switch to the layer)
+}
+
+#[allow(dead_code)]
 #[repr(u8)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum KeyCode {
+pub enum HidKey {
     No = 0x00,
 
     // Letters
@@ -108,65 +124,142 @@ pub enum KeyCode {
     RightMeta = 0xE7,
 }
 
-impl KeyCode {
+impl HidKey {
     pub const fn as_u8(self) -> u8 {
         self as u8
     }
 
     pub const fn is_modifier(self) -> bool {
         matches!(self,
-            KeyCode::LeftCtrl | KeyCode::LeftShift | KeyCode::LeftAlt | KeyCode::LeftMeta |
-            KeyCode::RightCtrl | KeyCode::RightShift | KeyCode::RightAlt | KeyCode::RightMeta
+            HidKey::LeftCtrl | HidKey::LeftShift | HidKey::LeftAlt | HidKey::LeftMeta |
+            HidKey::RightCtrl | HidKey::RightShift | HidKey::RightAlt | HidKey::RightMeta
         )
     }
 
     pub const fn modifier_bit(self) -> u8 {
         match self {
-            KeyCode::LeftCtrl => 0x01,
-            KeyCode::LeftShift => 0x02,
-            KeyCode::LeftAlt => 0x04,
-            KeyCode::LeftMeta => 0x08,
-            KeyCode::RightCtrl => 0x10,
-            KeyCode::RightShift => 0x20,
-            KeyCode::RightAlt => 0x40,  // AltGr
-            KeyCode::RightMeta => 0x80,
+            HidKey::LeftCtrl => 0x01,
+            HidKey::LeftShift => 0x02,
+            HidKey::LeftAlt => 0x04,
+            HidKey::LeftMeta => 0x08,
+            HidKey::RightCtrl => 0x10,
+            HidKey::RightShift => 0x20,
+            HidKey::RightAlt => 0x40,  // AltGr
+            HidKey::RightMeta => 0x80,
             _ => 0,
         }
     }
 }
 
 /// Keymap for my 4x12 ortholinear keyboard
-/// Each position [row][col] maps to a USB HID scancode
-pub const KEYMAP: [[KeyCode; 12]; 4] = [
+/// Each position [row][col] on each layer maps to an action
+pub const KEYMAPS: [[[Action; COLS]; ROWS]; N_LAYERS] = [
     [
-        KeyCode::Escape,    KeyCode::Q,      KeyCode::W,     KeyCode::E,
-        KeyCode::R,         KeyCode::T,      KeyCode::Y,     KeyCode::U,
-        KeyCode::I,         KeyCode::O,      KeyCode::P,     KeyCode::Backspace,
+        // base layer
+        [
+            Action::Key(HidKey::Escape),    Action::Key(HidKey::Q),      Action::Key(HidKey::W),     Action::Key(HidKey::E),
+            Action::Key(HidKey::R),         Action::Key(HidKey::T),      Action::Key(HidKey::Y),     Action::Key(HidKey::U),
+            Action::Key(HidKey::I),         Action::Key(HidKey::O),      Action::Key(HidKey::P),     Action::Key(HidKey::Backspace),
+        ],
+        [
+            Action::Key(HidKey::Tab),       Action::Key(HidKey::A),      Action::Key(HidKey::S),         Action::Key(HidKey::D),
+            Action::Key(HidKey::F),         Action::Key(HidKey::G),      Action::Key(HidKey::H),         Action::Key(HidKey::J),
+            Action::Key(HidKey::K),         Action::Key(HidKey::L),      Action::Key(HidKey::Semicolon), Action::Key(HidKey::Enter),
+        ],
+        [
+            Action::Key(HidKey::LeftShift), Action::Key(HidKey::Z),      Action::Key(HidKey::X),     Action::Key(HidKey::C),
+            Action::Key(HidKey::V),         Action::Key(HidKey::B),      Action::Key(HidKey::N),     Action::Key(HidKey::M),
+            Action::Key(HidKey::Comma),     Action::Key(HidKey::Dot),    Action::Key(HidKey::Up),    Action::Key(HidKey::Slash),
+        ],
+        [
+            Action::Key(HidKey::LeftCtrl),        Action::Layer(LayerOperation::MO(3)),     Action::Key(HidKey::LeftMeta), Action::Key(HidKey::LeftAlt),
+            Action::Layer(LayerOperation::MO(1)), Action::Key(HidKey::Space),               Action::Key(HidKey::No),       Action::Layer(LayerOperation::MO(2)),
+            Action::Key(HidKey::RightAlt),        Action::Key(HidKey::Left),                Action::Key(HidKey::Down),     Action::Key(HidKey::Right),
+        ],
     ],
+    // layer 1 (numbers mostly)
     [
-        KeyCode::Tab,       KeyCode::A,      KeyCode::S,         KeyCode::D,
-        KeyCode::F,         KeyCode::G,      KeyCode::H,         KeyCode::J,
-        KeyCode::K,         KeyCode::L,      KeyCode::Semicolon, KeyCode::Enter,
+        [
+            Action::Key(HidKey::Grave), Action::Key(HidKey::Kb1), Action::Key(HidKey::Kb2), Action::Key(HidKey::Kb3),
+            Action::Key(HidKey::Kb4),   Action::Key(HidKey::Kb5), Action::Key(HidKey::Kb6), Action::Key(HidKey::Kb7),
+            Action::Key(HidKey::Kb8),   Action::Key(HidKey::Kb9), Action::Key(HidKey::Kb0), Action::Trans,
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Key(HidKey::RightShift),
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+        ],
     ],
+    // layer 2 (additional keys missing from the kb)
     [
-        KeyCode::LeftShift, KeyCode::Z,      KeyCode::X,     KeyCode::C,
-        KeyCode::V,         KeyCode::B,      KeyCode::N,     KeyCode::M,
-        KeyCode::Comma,     KeyCode::Dot,    KeyCode::Up,    KeyCode::Slash,
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Key(HidKey::LeftBracket), Action::Key(HidKey::RightBracket), Action::Trans,
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Key(HidKey::Minus), Action::Key(HidKey::Equal), Action::Key(HidKey::Quote), Action::Trans,
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Key(HidKey::RightShift),
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+        ],
     ],
+    // layer 3 (fn key layer, with f* keys and home/end/pgup/pgdown)
     [
-        KeyCode::LeftCtrl,  KeyCode::No,     KeyCode::LeftMeta, KeyCode::LeftAlt,
-        KeyCode::No,        KeyCode::Space,  KeyCode::No,       KeyCode::No,
-        KeyCode::RightAlt,  KeyCode::Left,   KeyCode::Down,     KeyCode::Right,
+        [
+            Action::Key(HidKey::F1), Action::Key(HidKey::F2), Action::Key(HidKey::F3), Action::Key(HidKey::F4),
+            Action::Key(HidKey::F5), Action::Key(HidKey::F6), Action::Key(HidKey::F7), Action::Key(HidKey::F8),
+            Action::Key(HidKey::F9), Action::Key(HidKey::F10), Action::Key(HidKey::F11), Action::Key(HidKey::F12),
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Key(HidKey::PageUp), Action::Trans,
+        ],
+        [
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Trans, Action::Trans, Action::Trans,
+            Action::Trans, Action::Key(HidKey::Home), Action::Key(HidKey::PageDown), Action::Key(HidKey::End),
+        ],
     ],
 ];
 
-/// Get keycode from given row and column
-pub fn get_keycode(row: usize, col: usize) -> Option<KeyCode> {
-    if row < 4 && col < 12 {
-        let keycode = KEYMAP[row][col];
-        if keycode != KeyCode::No {
-            return Some(keycode);
+/// Get action from given row and column
+pub fn get_action(row: usize, col: usize, layer: usize) -> Action {
+    if row < ROWS && col < COLS && layer < N_LAYERS {
+        let action = KEYMAPS[layer][row][col];
+
+        // handle transparent keys, in this case it should fall down to the first layer without transparent key
+        if matches!(action, Action::Trans) && layer > 0 {
+            return get_action(row, col, layer - 1);
         }
+        
+        action
+    } else {
+        Action::None
     }
-    None
 }
diff --git a/src/main.rs b/src/main.rs
index cd5207c..deb5fea 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -17,9 +17,9 @@ use embassy_rp::{
 };
 use embassy_time::{Duration, Timer};
 use usbd_hid::descriptor::KeyboardReport;
-use {defmt_rtt as _, panic_probe as _};
+use crate::keymap::{Action, LayerOperation, get_action};
 
-use keymap::get_keycode;
+use {defmt_rtt as _, panic_probe as _};
 
 bind_interrupts!(struct Irqs {
     I2C0_IRQ => I2cInterruptHandler<embassy_rp::peripherals::I2C0>;
@@ -68,18 +68,45 @@ async fn main(_spawner: Spawner) -> () {
     let in_fut = async {
         let mut previous_keycodes: [u8; 6] = [0; 6];
         let mut previous_modifier: u8 = 0;
+        let mut active_layer: usize = 0;
 
         loop {
             let scan_result = matrix.scan().await;
 
-            // Collect all pressed keys and their scancodes
-            let mut pressed_keys: heapless::Vec<(usize, usize, keymap::KeyCode), 48> = heapless::Vec::new();
+            // first pass to check if the layer keys are active
+            let mut layer_active = false;
 
             for (row_idx, row) in scan_result.iter().enumerate() {
                 for (col_idx, &is_pressed) in row.iter().enumerate() {
                     if is_pressed {
-                        if let Some(keycode) = get_keycode(row_idx, col_idx) {
-                            let _ = pressed_keys.push((row_idx, col_idx, keycode));
+                        // try to find if any of the pressed keys on the 0th layer is a layer modify key
+                        let action = get_action(row_idx, col_idx, 0);
+                        if let Action::Layer(LayerOperation::MO(layer)) = action {
+                            layer_active = true;
+                            active_layer = layer;
+                            break;
+                        }
+                    }
+                }
+                // break the loop early if layer key is pressed
+                if layer_active {
+                    break;
+                }
+            }
+
+            if !layer_active {
+                active_layer = 0;
+            }
+
+            // Collect all pressed keys and their scancodes
+            let mut pressed_keys: heapless::Vec<(usize, usize, keymap::Action), 48> = heapless::Vec::new();
+
+            for (row_idx, row) in scan_result.iter().enumerate() {
+                for (col_idx, &is_pressed) in row.iter().enumerate() {
+                    if is_pressed {
+                        let action = get_action(row_idx, col_idx, active_layer);
+                        if !matches!(action, Action::None | Action::Layer(_)) {
+                            let _ = pressed_keys.push((row_idx, col_idx, action));
                         }
                     }
                 }
@@ -90,14 +117,16 @@ async fn main(_spawner: Spawner) -> () {
             let mut keycodes = [0u8; 6];
             let mut keycode_index = 0;
 
-            for (_, _, keycode) in pressed_keys.iter() {
-                if keycode.is_modifier() {
-                    // Add to modifier byte
-                    modifier |= keycode.modifier_bit();
-                } else if keycode_index < 6 {
-                    // Add to keycodes array (max 6 regular keys)
-                    keycodes[keycode_index] = keycode.as_u8();
-                    keycode_index += 1;
+            for (_, _, action) in pressed_keys.iter() {
+                if let Action::Key(hid_key) = action {
+                    if hid_key.is_modifier() {
+                        // Add to modifier byte
+                        modifier |= hid_key.modifier_bit();
+                    } else if keycode_index < 6 {
+                        // Add to keycodes array (max 6 regular keys)
+                        keycodes[keycode_index] = hid_key.as_u8();
+                        keycode_index += 1;
+                    }
                 }
             }