The field of gas phase reaction dynamics is primarily concerned with understanding how the microscopic forces between atoms and molecules govern chemical reactivity. This goal is targeted by performing exacting experiments which yield measurements of detailed attributes of chemical reactions, and by developing stateof-the-art theoretical techniques in order to calculate accurate potential energy surfaces for reactions and determine the molecular dynamics that occur on these surfaces. It has recently become possible to compare experimental results with theoretical predictions on a series of benchmark reactions. This convergence of experiment and theory is leading to significant breakthroughs in our understanding of how the peaks and valleys on a potential energy surface can profoundly affect the measurable properties of a chemical reaction.