A fixture is a device used in machining, inspection, assembly, welding, and other manufacturing operations to locate and hold a workpiece firmly in position so that the required manufacturing processes can be carried out corresponding to design specifications (Nee and Senthil Kumar, 1991). As part of manufacturing tooling, fixture design and related activities make significant contributions to the production time and cost in daily production. In this chapter, basic fixture-design requirements are first discussed, the lo cating principle and locating error analysis are presented in detail, and clamping devices and clamping-force estimation are introduced. These prin ciples and discussions are valid for general fixture designs and are not lim ited to modular-fixture applications. Advanced, computerized fixture design and analysis is not included in this chapter.