Over the past six decades, Hatch has been engaged in design, development, and construction of many engineering projects in the mining, metals, and chemicals industries. Throughout those projects, Hatch engineers have helped their clients to transform exploratory stage of projects to their commercialization through the most economical processes. To support such transformations, Hatch has planned, designed, and executed numerous successful testwork programs at laboratory scale, pilot plant, and demonstration plant scales. The development of a sound metallurgical testwork program provides a semi-empirical method (based on both theoretical research and practical experience) to supply reliable design data to select and size process equipment and create a profitable and feasible process flowsheet. In this paper, an introduction to metallurgical testwork programs, the main reason to perform such tests, and related methods are presented. It is followed by a discussion of some practical cases from Hatch’s years of experience, from which a framework for testwork planning at the various stages of engineering was developed. Finally, in order to provide a thorough understanding of metallurgical testwork programs, possible reasons for the success or failures of testwork programs are discussed.