This paper reviews the essential results of our research on the deformation behavior of fully lamellar microstructures under compressive loading. The most important outcomes, experimentally and theoreticaly, are presented. Usually such fully lamellar microstructures are present in cast intermetallic γ(TiAl)-based alloys; therefore, this class of materials was selected to verify the developed model. During large compressive deformation of γ(TiAl)-based alloys at elevated temperatures the lamellar colonies, depending on their orientation, are often bent or buckled which is representative of a deformation “instability” characterized by a large wave length. Structural defects of the lamellae as well as their somewhat irregular arrangement trigger such a deformation behavior. In addition, kink formation and shear band-type deformation modes occur according to an “instability” mode exhibiting a short wave length. These two deformation modes interact in a rather subtle way, which leads to a very inhomogeneous deformation pattern. A short paragraph on the stability behavior of composites is, therefore, added.