In this chapter, we introduced the mass production testing of products based on Espressif's modules and chips, and the burning of mass production firmware, so that readers can have a preliminary understanding of mass production. For devices to be identified and bound to users, unique mass production data must be burned to each device. To save manufacturers' trouble of burning firmware in mass production, Espressif provides modules with customized firmware, which can be mounted directly onto the product's hardware circuit.