This chapter discusses the stability and behavior of columns under compressive loads. It begins by introducing columns and their goals of studying stability, critical load, effective length, and the secant formula. It then covers the stability of structures and Euler's formula for pin-ended columns. Subsequent sections extend Euler's formula to other end conditions, discuss eccentric loading and the secant formula, and address design of columns under centric and eccentric loads using empirical equations and allowable stress or load resistance factor approaches.