diff --git a/Makefile.dev b/Makefile.dev
index e4e438a..f5cf687 100644
--- a/Makefile.dev
+++ b/Makefile.dev
@@ -1,6 +1,6 @@
 TARGET ?= forge
 INSTALL_DIR ?= $(HOME)/.local/bin
-TEST_ARGS ?= --frag=./shaders --config=./config/forge.cfg --video-in=/dev/video0 --video-in=/dev/video1 --video-in=/dev/video2 --video-in=/dev/video3 --video-in=/dev/video4 --video-in=/dev/video5 --video-in=/dev/video6 --video-in=/dev/video7 --video-in=/dev/video8 --video-in=/dev/video9 --tempo=30
+TEST_ARGS ?= --frag=./shaders --config=./config/forge.cfg --video-in=/dev/video0 --video-in=/dev/video1 --video-in=/dev/video2 --video-in=/dev/video3 --video-in=/dev/video4 --video-in=/dev/video5 --video-in=/dev/video6 --video-in=/dev/video7 --video-in=/dev/video8 --video-in=/dev/video9
 SHELL := /bin/bash
 
 .PHONY: build
diff --git a/README.md b/README.md
index e2af5e9..f730505 100644
--- a/README.md
+++ b/README.md
@@ -133,7 +133,7 @@ make -f Makefile.dev release-arch
   - [x] Send midi data to shaders
   - [ ] Save midi state
   - [x] State machine with A/B switch
-  - [ ] Tap-tempo feature
+  - [x] Tap-tempo feature
   - [ ] Clean code and fix things
 - [x] Video input
   - [x] Fixed camera video
@@ -151,5 +151,6 @@ make -f Makefile.dev release-arch
   - [x] Clean code and fix things
   - [x] Share openGL state between monitor and screen
 - [ ] Other
+  - [ ] Update readme with usage documentation
   - [ ] Clone "shaders" and config in system path at setup
   - [ ] Find and fix opengl errors 0500 ?
\ No newline at end of file
diff --git a/src/config.h b/src/config.h
index f15fbe9..660aed4 100644
--- a/src/config.h
+++ b/src/config.h
@@ -1,6 +1,8 @@
 #ifndef CONFIG_H
 #define CONFIG_H
 
+/* PACKAGE */
+
 #ifndef PACKAGE
 #define PACKAGE "forge"
 #endif /* PACKAGE */
@@ -9,6 +11,8 @@
 #define VERSION "(dev)"
 #endif /* VERSION */
 
+/* TYPES */
+
 #ifndef MAX_VIDEO
 #define MAX_VIDEO 16
 #endif
@@ -17,6 +21,8 @@
 #define MAX_FRAG 64
 #endif
 
+/* MIDI */
+
 #ifndef UNSET_MIDI_CODE
 #define UNSET_MIDI_CODE 300
 #endif
@@ -25,6 +31,8 @@
 #define MIDI_MAX 127
 #endif
 
+/* ARRAY */
+
 #ifndef ARRAY_SIZE
 #define ARRAY_SIZE 1024
 #endif
@@ -33,4 +41,36 @@
 #define ARRAY_NOT_FOUND ARRAY_SIZE + 1
 #endif
 
+/* TEMPO */
+
+#ifndef MAX_BEAT_LENGTH
+// 30.0 bpm
+#define MAX_BEAT_LENGTH 2000
+#endif
+
+#ifndef MIN_BEAT_LENGTH
+// 240.0 bpm
+#define MIN_BEAT_LENGTH 250
+#endif
+
+#ifndef BEATS_UNTIL_CHAIN_RESET
+#define BEATS_UNTIL_CHAIN_RESET 3
+#endif
+
+#ifndef TOTAL_TAP_VALUES
+#define TOTAL_TAP_VALUES 8
+#endif
+
+#ifndef SKIPPED_TAP_THRESHOLD_LOW
+#define SKIPPED_TAP_THRESHOLD_LOW 1.75
+#endif
+
+#ifndef SKIPPED_TAP_THRESHOLD_HIGH
+#define SKIPPED_TAP_THRESHOLD_HIGH 2.75
+#endif
+
+#ifndef MAX_TAP_VALUES
+#define MAX_TAP_VALUES 10
+#endif
+
 #endif /* CONFIG_H */
\ No newline at end of file
diff --git a/src/forge.c b/src/forge.c
index 1e4a07e..c8cb8c1 100644
--- a/src/forge.c
+++ b/src/forge.c
@@ -1,10 +1,11 @@
 #include <log.h>
 #include <math.h>
 #include <stdbool.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/wait.h>
 
-#include "arr.h"
 #include "config.h"
 #include "config_file.h"
 #include "file.h"
@@ -14,6 +15,7 @@
 #include "shaders.h"
 #include "shared.h"
 #include "state.h"
+#include "tempo.h"
 #include "timer.h"
 #include "types.h"
 #include "video.h"
@@ -58,7 +60,8 @@ static void init_context(Parameters params, unsigned int in_count,
                          unsigned int frag_count) {
   unsigned int i;
 
-  context->tempo = params.base_tempo;
+  context->tempo = tempo_init();
+  tempo_set(&context->tempo, params.base_tempo);
   context->demo = params.demo;
   context->monitor = params.monitor;
 
diff --git a/src/shaders.c b/src/shaders.c
index 60d32b2..2002a4b 100644
--- a/src/shaders.c
+++ b/src/shaders.c
@@ -514,7 +514,7 @@ static void use_program(ShaderProgram program, int i, bool output,
   }
   // set fragment uniforms
   write_uniform_1f(program.itime_locations[i], context->time);
-  write_uniform_1f(program.itempo_locations[i], context->tempo);
+  write_uniform_1f(program.itempo_locations[i], context->tempo.tempo);
   write_uniform_1i(program.ifps_locations[i], context->fps);
   write_uniform_1i(program.idemo_locations[i], context->demo ? 1 : 0);
   write_uniform_1i(program.ipage_locations[i], context->page);
diff --git a/src/state.c b/src/state.c
index a90799f..6d2bba8 100644
--- a/src/state.c
+++ b/src/state.c
@@ -6,6 +6,7 @@
 #include "midi.h"
 #include "rand.h"
 #include "state.h"
+#include "tempo.h"
 #include "types.h"
 
 StateConfig state_parse_config(ConfigFile config) {
@@ -250,6 +251,14 @@ void state_apply_event(SharedContext *context, StateConfig state_config,
     }
   }
 
+  if (code == state_config.tap_tempo_code) {
+    found = true;
+    midi_write(midi, code, value);
+    if (value > 0) {
+      tempo_tap(&context->tempo);
+    }
+  }
+
   if (!found) {
     log_trace("unknown midi: %d %d", code, value);
     midi_write(midi, code, value);
@@ -261,6 +270,7 @@ void state_apply_event(SharedContext *context, StateConfig state_config,
 bool state_background_midi_write(SharedContext *context,
                                  StateConfig state_config, MidiDevice midi) {
   pid_t pid;
+  bool beat_active, last_active;
 
   pid = fork();
   if (pid < 0) {
@@ -276,8 +286,21 @@ bool state_background_midi_write(SharedContext *context,
   update_active(context, state_config, midi);
   update_values(context, state_config, midi);
 
+  last_active = false;
+
   while (!context->stop) {
-    // TODO tap tempo and more
+    beat_active = tempo_progress(context->tempo) < 0.25;
+
+    if (beat_active != last_active) {
+      safe_midi_write(midi, state_config.tap_tempo_code,
+                      beat_active ? MIDI_MAX : 0);
+
+      safe_midi_write(midi,
+                      state_config.select_frag_codes.values[context->selected],
+                      beat_active ? MIDI_MAX : 0);
+
+      last_active = beat_active;
+    }
   }
 
   log_info("(state) background writing stopped by main thread (pid: %d)", pid);
diff --git a/src/tempo.c b/src/tempo.c
index 8298b33..a23f6dc 100644
--- a/src/tempo.c
+++ b/src/tempo.c
@@ -1 +1,122 @@
-#include "tempo.h"
\ No newline at end of file
+#include <math.h>
+#include <string.h>
+#include <sys/time.h>
+
+#include "config.h"
+#include "log.h"
+#include "tempo.h"
+
+static long now() {
+  struct timeval now;
+
+  gettimeofday(&now, NULL);
+
+  return now.tv_sec * 1000 + now.tv_usec / 1000;
+}
+
+static void reset_tap_chain(Tempo *tempo, long t) {
+  tempo->last_reset = t;
+  tempo->last_tap = 0;
+  tempo->taps_in_chain = 0;
+  tempo->tap_duration_index = 0;
+  tempo->last_tap_skipped = false;
+
+  memset(tempo->tap_durations, 0, sizeof(tempo->tap_durations));
+}
+
+Tempo tempo_init() {
+  Tempo tempo;
+  long t;
+
+  t = now();
+
+  reset_tap_chain(&tempo, t);
+
+  return tempo;
+}
+
+static bool is_chain_active(Tempo tempo, long t) {
+  return tempo.last_tap + MAX_BEAT_LENGTH > t &&
+         tempo.last_tap + (tempo.beat_length * BEATS_UNTIL_CHAIN_RESET) > t;
+}
+
+static unsigned long get_average_tap_duration(Tempo tempo) {
+  unsigned int amount, i;
+  unsigned long running_total, average_tap_duration;
+
+  amount = tempo.taps_in_chain - 1;
+  if (amount > TOTAL_TAP_VALUES) {
+    amount = TOTAL_TAP_VALUES;
+  }
+
+  running_total = 0;
+  for (i = 0; i < amount; i++) {
+    running_total += tempo.tap_durations[i];
+  }
+
+  average_tap_duration = running_total / amount;
+  if (average_tap_duration < MIN_BEAT_LENGTH) {
+    log_debug("%ld", average_tap_duration);
+    return MIN_BEAT_LENGTH;
+  }
+
+  return average_tap_duration;
+}
+
+static void add_tap_to_chain(Tempo *tempo, long t) {
+  long duration;
+
+  duration = t - tempo->last_tap;
+
+  tempo->last_tap = t;
+
+  tempo->taps_in_chain++;
+
+  if (tempo->taps_in_chain == 1) {
+    return;
+  }
+
+  if (tempo->taps_in_chain > 2 && !tempo->last_tap_skipped &&
+      duration > tempo->beat_length * SKIPPED_TAP_THRESHOLD_LOW &&
+      duration < tempo->beat_length * SKIPPED_TAP_THRESHOLD_HIGH) {
+    duration = duration >> 1;
+    tempo->last_tap_skipped = true;
+  } else {
+    tempo->last_tap_skipped = false;
+  }
+
+  tempo->tap_durations[tempo->tap_duration_index++] = duration;
+
+  if (tempo->tap_duration_index == TOTAL_TAP_VALUES) {
+    tempo->tap_duration_index = 0;
+  }
+
+  tempo->beat_length = get_average_tap_duration(*tempo);
+
+  tempo->tempo = 60000.0 / tempo->beat_length;
+}
+
+void tempo_set(Tempo *tempo, float value) {
+  tempo->tempo = value;
+  tempo->beat_length = 60000.0 / value;
+}
+
+void tempo_tap(Tempo *tempo) {
+  long t;
+
+  t = now();
+
+  if (!is_chain_active(*tempo, t)) {
+    reset_tap_chain(tempo, t);
+  }
+
+  add_tap_to_chain(tempo, t);
+}
+
+double tempo_progress(Tempo tempo) {
+  long t;
+
+  t = now();
+
+  return fmod((double)(t - tempo.last_reset) / (double)tempo.beat_length, 1.0);
+}
\ No newline at end of file
diff --git a/src/tempo.h b/src/tempo.h
index 396eda4..7cd0af5 100644
--- a/src/tempo.h
+++ b/src/tempo.h
@@ -3,4 +3,12 @@
 #ifndef TEMPO_H
 #define TEMPO_H
 
+Tempo tempo_init();
+
+void tempo_tap(Tempo *tempo);
+
+void tempo_set(Tempo *tempo, float value);
+
+double tempo_progress(Tempo tempo);
+
 #endif /* TEMPO_H */
\ No newline at end of file
diff --git a/src/types.h b/src/types.h
index c412c2b..763a087 100644
--- a/src/types.h
+++ b/src/types.h
@@ -135,6 +135,17 @@ typedef ARRAY(VideoCaptureArray, VideoCapture);
 
 typedef GLFWwindow Window;
 
+typedef struct Tempo {
+  long last_reset;
+  long last_tap;
+  unsigned int taps_in_chain;
+  unsigned int tap_duration_index;
+  unsigned int tap_durations[MAX_TAP_VALUES];
+  bool last_tap_skipped;
+  unsigned long beat_length;
+  float tempo;
+} Tempo;
+
 typedef struct SharedContext {
   int fd;
 
@@ -145,7 +156,7 @@ typedef struct SharedContext {
   unsigned int internal_height;
   double time;
   unsigned int fps;
-  float tempo;
+  Tempo tempo;
   // TODO use array
   unsigned int state[MAX_FRAG];
   unsigned int page;
diff --git a/src/video.c b/src/video.c
index 7eed535..5e6e318 100644
--- a/src/video.c
+++ b/src/video.c
@@ -4,14 +4,13 @@
 #include <log.h>
 #include <stdbool.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
 
-#include "shared.h"
 #include "timer.h"
 #include "types.h"
 #include "video.h"
-#include "window.h"
 
 static void ioctl_error(VideoCapture *video_capture, const char *operation,
                         const char *default_msg) {