Hi, Let me expose my problem : I have to rotate an object. But I have met the ''Gembal Lock'', using Euler angles with glRotatef(). So I read an article (http://www.gamedev.net/reference/articles/article1095.asp) to get rid of this by using quaternions, but my problem is still there ! Here is what I do : get the angle (in Euler axis) to rotate (from mouse). convert the angle to a quaternion. multiply this quaternion with the rotation quaternion of the object. this gives a new rotation quaternion for the object. then this quaternion is transformed into a new rotation matrix (4x4). finally, glMultMatrix() is called with the new matrix. Every thing works but I still have the Gembal Lock !!! In the article, it is said that quaternions are not supposed to have the Gimbal Lock if the rotation are done by multiplying quaternions !! Please Help !! Thanks !