Transmission topology optimization (line switching) supports congestion management by routing power flow away from congested / overloaded facilities to the rest of the system which has spare capacity. The result is an increase in transfer capabilities from low-cost resources to demand centers with significant potential for economic and reliability benefits. However, due to the computational complexity of the problem, its use has been limited, employed on an ad-hoc basis and relying on operators’ previous experience or a set of fixed procedures. This lecture will discuss transmission topology optimization, including tractable, near-optimal approached to co-optimize transmission topology with generation dispatch and commitment. Simulation results on full models of PJM markets and operations will be presented.