diff --git a/client.c b/client.c
index 85b0f38..32c8338 100644
--- a/client.c
+++ b/client.c
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #include "client.h"
 
 // TODO
diff --git a/client.h b/client.h
index 19d2b95..ab04dfe 100644
--- a/client.h
+++ b/client.h
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #ifndef CLIENT_H
 #define CLIENT_H
 
diff --git a/handler.c b/handler.c
index 4b38a32..4734af8 100644
--- a/handler.c
+++ b/handler.c
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #include "handler.h"
 #include "wm.h"
 #include "client.h"
diff --git a/handler.h b/handler.h
index bca04c1..4a5467e 100644
--- a/handler.h
+++ b/handler.h
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #ifndef HANDLER_H
 #define HANDLER_H
 
diff --git a/main.c b/main.c
index 8aa74d4..b8e4a96 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #include "wm.h"
 
 int main(int argc, char **arg)
diff --git a/wm.c b/wm.c
index 208dd6b..18f2279 100644
--- a/wm.c
+++ b/wm.c
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #include "wm.h"
 #include <X11/X.h>
 #include <X11/Xatom.h>
diff --git a/wm.h b/wm.h
index 12b218e..60531d2 100644
--- a/wm.h
+++ b/wm.h
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #ifndef WM_H
 #define WM_H
 
diff --git a/wmc.c b/wmc.c
index f77e1d6..f68d976 100644
--- a/wmc.c
+++ b/wmc.c
@@ -1,3 +1,22 @@
+/*
+The GPLv3 License (GPLv3)
+
+Copyright (c) 2022 Akos Horvath
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>