In the context of molecular reaction dynamics, the study of elementary reactions with excited species has developed rapidly in the last decades. This article reviews recent developments in the study of reactive collisions with excited-state atoms, under single-collision conditions provided by crossed-beam and low-pressure gas cell experiments. Application of high-resolution laser techniques allows selective electronic excitation of atomic reagents. This excitation is used to identify the key features of state-selected and spin-orbit effects, on both the reaction cross-sections and product state distributions. The polarized nature of the laser field is used to gain a detailed understanding of the reaction dynamics and stereodynamics, through the alignment of atomic orbitals. Several examples are discussed in the light of current theoretical models, a detailed analysis of the data leading to the identification of non-adiabatic processes taking place on excited potential-energy surfaces. New experimental developments will allow for an even deeper understanding of these elementary processes.