The study of structural instability plays a role of primary importance in the field of applied mechanics. Despite the remarkable progresses made in the recent past years, the structural instability remains one of the most challenging topics in applied - chanics. Many problems have bee:: solved in the last decades but still many others remain to be solved satisfactorily. The increasing number of papers published in jo- nals and conferences organized by ECCS, SSRC, IUTAM, and EUROMECH strongly indicates the interest of scientists and engineers in the subject. A careful examination of these publications shows that they tend to fall into one of the two categories. The first is that of practical design direction in which methods for analyzing specific stability problems related to some specific structural typologies are developed. The research works are restricted to determining the critical load, considering that it is sufficient to kw the limits of stability range. These studies are invaluable since their aim is to provide solutions to practical problems, to supply the designer with data useful for design and prepare rms, specifications and codes. The second direction is that of theoretical studies, aiming at a mathematical modeling of the instability problems, for a better understanding of the phemena. In these studies, special emphasis is placed on the behavior of structures after the loss of stability in the post-critical range. This approach is less familiar to designers as its results have t yet become part of current structural design practice.