With the maturity of conceptual fusion reactor designs it is important to develop comprehensive scenarios for the startup and shutdown of fusion plants and to investigate physics and engineering requirements and design constraints and their implications. We then focus on the impact of such considerations on the operation of tandem mirror fusion reactors (TMR's). Brief examples from both the fission and conventional power industries are discussed. TMR plant operation is divided into an initial commissioning phase and four subsequent generic phases: (1) Phase IA: cold shutdown; (2) Phase IB: hot shutdown; (3) Phase II: system testing, plasma startup and standby power operation; (4) Phase III: staged power operation; and (5) Phase IV: rated power operation. Power ascention through these phases is explained in terms of the operation of two major systems: (1) the plasma technology and support system, and (2) the heat transport system. Physics and engineering constraints, subsystem interactions, and design implications are discussed throughout the paper using the Mirror Advanced Reactor Study (MARS) as the specific example.