Chemical reactions at the gas–surface interface are ubiquitous in the chemical industry as well as in nature. Investigating these processes at a microscopic, quantum state–resolved level helps develop a predictive understanding of this important class of reactions. In this review, we present an overview of the field of quantum state–resolved gas–surface reactivity measurements that explore the role of the initial quantum state on the dissociative chemisorption of a gas-phase reactant incident on a solid surface. Using molecular beams and either quantum state–specific reactant preparation or product detection by laser excitation, these studies have observed mode specificity and bond selectivity as well as steric effects in chemisorption reactions, highlighting the nonstatistical and complex nature of gas–surface reaction dynamics.