It is well known that a building frame, unrestrained against sidesway at the floor levels, may buckle as a unit in the lateral direction when the applied load has reached a certain critical value.This phenomenon is often referred to as frame instability. A great deal of research work has been done on this problem in the past, and numerous methods are now available for obtaining exact and/or approximate solutions.This paper contains a general survey of the various frame instability theories, discussions of several recent papers, and a review of current and future research trends.A list of references and summaries of solutions for some practical frames are also included.