Launch success involves detailed multi-disciplined engineering during all phases of a liquid rocket engine – development, production, and operation. The development phase starts with system requirements and involves extensive testing and evaluation to characterize and qualify engine design and operation. Upon completion of development, an engine goes into full-scale production. Each production engine must meet its requirements within allowable engine-to-engine variations, typically during acceptance testing. Every risk must be understood, accepted or mitigated. Numerous reviews, tests and inspections are performed to verify compliance with requirements throughout the entire production process, from component fabrication to vehicle integration. The overall operation of a liquid rocket engine is divided into four distinct stages: (i) start-up transient, (ii) steady state, (iii) throttling (if throttleable), and (iv) shutdown transient. Start and shutdown transients expose engine components to extreme gradients in operating conditions, while steady-state and throttling operations occur for a majority of flight and involve fairly moderate changes in operating conditions. This chapter will provide a general overview of the production and operation of liquid rocket engines. Manufacturing and acceptance testing will be discussed as well as vehicle integration and flight operation. Examples of three actual operational engines will also be provided. Keywords: liquid propulsion; liquid rocket engine; manufacturing; production; acceptance testing; hot firing; vehicle integration; engine operation; launch