This chapter explores the significant influence of full quantum effects on chemical reactions, surpassing the framework of classical transition-state theory (TST). For light element systems (e.g., H2, O2), quantum tunneling, vibration, and electron–nucleus quantum coupling have decisive impacts on the reaction process. Advancements in reaction rate theory incorporate tunneling and zero-point energy into TST, while the field waits for the development of a more comprehensive TST that precisely treats full quantum effects. Nuclear quantum effect is critical in hydrogen dynamics at room temperatures (even above 500 K), ultracold reactions, penning discharge, nonclassical product formation in organic reactions, performance improvement in electrolysis utilizing kinetic isotope effects (e.g., in aqueous batteries), and biochemical reactions. Quantum tunneling is likely to facilitate the origin of life at its early stage by increasing the rate of forming organic molecules. Nonadiabatic effects (NAEs) manifest in altering electronic eigenstate population (e.g., relaxation dynamics) and dynamic nuclear transfer between split potential energy surfaces (e.g., chlorine–hydrogen collision, water photodissociation), demonstrated or indicated by experiment or theoretical calculation.