This chapter provides an overview of variational transition state theory from the perspective of the dynamical formulation of the theory. Transition state theory (TST) is a theoretical framework for calculating and interpreting rate constants of chemical reactions. TST was formulated nearly 70 years ago with the goal of providing a computational tool for predicting rate constants from knowledge of the potential energy surface controlling the reaction. This formulation provides a firm classical mechanical foundation for a quantitative theory of reaction rate constants, and it provides a sturdy framework for the consistent inclusion of corrections for quantum mechanical effects and the effects of condensed phases. A central construct of the theory is the dividing surface separating reaction and product regions of phase space. The chapter also focuses on the robust nature of the method offered by the flexibility of the dividing surface that allows the accurate treatment of a variety of systems from activated and barrier-less reactions in the gas phase, reactions in rigid environments, and reactions in liquids and enzymes.