The intense global competition to produce quality products at a low cost has led many industrial nations to consider mechanical tolerances as a key factor to bring about cost saving as well as to remain competitive. In the last two decades, some work has been done in the area of tolerance techniques. In this paper a comprehensive summary of the state-of-the-art and the projection of future trends in tolerancing techniques is presented to describe improved techniques available today and to aid in guiding research for the future. This paper reviews the status of theory and practice of how manufacturing and assembly processes are characterized for relating tolerancing to process or production cost. The specification of tolerancing on the dimension of the manufactured part has a significant impact on the final production cost. Tight tolerances can result in excessive process cost, while loose tolerances may lead to increased waste and assembly problems. This paper systematically reviews the state-of-the-art by classifying more than 50 papers written so far into five categories. They are, the dimensional tolerances chain technique, geometrical modelling in tolerances, statistical and probabilistic methods in tolerancing, tolerances based on analysis and synthesis, tolerances based on cost-tolerance algorithms and design methods. Future areas of research and the unresolved issues have been presented that will serve as a springboard for researchers to investigate and produce solutions for the end of this century. The present problems and issues once resolved, will revolutionize the manufacturing industry as the year 2000 approaches!