In order to fabricate dimensionally stable components the causes of dimensional instability must be understood and controlled to the level required by the specifications. This paper reviews four types of dimensional instability and the sources that cause dimensional change including the effects of external and internal stress on both macro- and micro-levels. Stress relief and stress relaxation as well as the use of low expansion materials are discussed. Examples are given of both unstable components and methods employed for fabricating stable components from materials such as aluminum beryllium glass and composites. 1.