IN PREPARATION OF THIS CHAPTER, THE CONtents of the fourteenth edition were extensively drawn upon. The authors acknowledge the author of the fourteenth edition, Mark P. Morse. The current edition will review and update the topics as addressed by the previous author, introduce new technology that has been developed, and include up-to-date references. This chapter is an abridged and modified version of the chapter entitled “Flexibility,” written by Garmond G. Schurr, found in earlier editions of this manual.