An overview is given of approximate effective length formulas. The overview is limited to formulas that are relevant for the important class of compression members defined by constant stiffness and constant axial force along the length, and, furthermore, limited to members that are either completely unbraced (with zero shear and free-sway) or fully braced against lateral translation of one end relative to the other. Whereas most approximate effective length formulas have been developed for positive end restraints, buckling modes of compression members in a frame can be associated with both positive and negative end restraints. It is a main concern of the study to identify the applicability of the various approximate formulas for a reasonable wide range of positive and negative restraint combinations. Extensive comparisons of approximate predictions with exact effective length results have been carried out.