Power systems planning and operations is one of the most challenging problems in energy field due to its complex, large-scale and nonlinear nature. Operating power systems with uncertainties and disturbances such as failure of system components increases complexity and causes difficulties in sustaining a supplydemand balance in power systems without jeopardizing grid reliability. To handle with the uncertainties and operate power systems without endangering grid reliability, utilities and system operators implement various control mechanisms such as energy storage, transmission switching, renewable energy curtailment and demand-side management. In this thesis, we first propose a multi-period mathematical programming model to discuss the effect of transmission switching decisions on power systems expansion planning problems. We then explore the value of control mechanisms for integrating renewable energy sources into power systems. We develop a two-stage stochastic programming model that cooptimizes investment decisions and transmission switching operations. Later, we analyze the effect of demand-side management programs on peak load management. We provide a conceptual framework for quantifying the incentives paid to the consumers to reshape their load profiles while taking hourly electrical power generation costs as reference points. Finally, we study reliability aspect of the power system planning and consider unexpected failures of components. We provide a two-stage stochastic programming model and discuss value of transmission switching on grid reliability.