During the past ten years, the relaxation of international tensions between East and West has resulted in the so-called peace dividendsº. Among these dividends, solid state physicists have profited from the increasing availability of stable isotopes of many elements at affordable prices. These isotopes originate sometimes in the United States and sometimes in Russia. They can either be purchased or obtained on loanº on the basis of scientific collaboration. With these isotopes, single crystals with tailor-made isotopic compositions have been grown. Using these crystals, information on a number of rather basic physical properties has been obtained. We discuss in this review the following properties of such semiconductor crystals: 1. dependence of the lattice parameters on isotopic masses; 2. effect of isotopic disorder on thermal conductivity; 3. anharmonic effects on the phonon frequencies and linewidths and their dependence on isotopic mass; 4. effects of isotopic disorder on phonon frequencies and linewidhts; 5. renormalization of the energy of electronic states through electron±phonon interaction; and 6. self-diffusion of atoms in crystals. Because of space limitations this discussion will not be exhaustive. We hope, however, to give sufficient references to published work so that the interested reader can easily find the primary literature sources to this rapidly expanding field of solid state physics. (A few multilingual short reviews are listed under [1].