Dry gas seals play a critical role in the performance of modern centrifugal compressorsCentrifugal compressor. However, specifying engineers often overlook the importance of clearly defining the scope and carefully selecting the most suitable seal type, its control system, and associated auxiliaries for the intended application. Instead, this responsibility is frequently deferred to compressor manufacturers, who make these selections based on their own standards. To ensure optimal design and performance, several key factors must be thoroughly evaluated—these include the gas composition, the thermodynamic properties of the seal or buffer gas, the choice of barrier gas, operational scenarios such as slow roll conditions, compatibility with bidirectional rotation, and overall system rating. Ideally, this evaluation should be a collaborative effort involving the equipment vendor, the seal manufacturer, and machinery engineers representing both the owner and the engineering contractor. Choosing the correct dry gas seal and its support system is essential for ensuring the long-term reliability and availability of centrifugal compressorCentrifugal compressor trains in process plants. This chapter explores several important aspects, including the operating principles of dry gas seal faces, techniques for controlling seal gas, procedures for slow rolling, and strategies for managing demanding sealing environments.