Defects and strains at surfaces and interfaces are examined with respect to how they can be measured and how they affect resulting magnetic, electronic or mechanical properties. Emphasis is on MnZn ferrite, GaAs and PbS with deformation being examined by selected area channeling pattern (SACP), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) techniques. Damage produced during preparation of magnetic surfaces is examined by broadening of lines in SACP patterns while epitaxial strains and their relaxations by dislocations are estimated using both line shifts of SACP patterns and direct imaging by TEM. Of particular importance is that a new SACP method with accuracy approaching 0.1 percent has been developed for non-destructive examination of epitaxial strains in InGaAs/GaAs. Also, for the first time microcrack features in a low band gap semiconductor have been examined with STM.