The modern zoo has been associated with two major behavioral welfare advances: (a) the use of training to increase voluntary husbandry care, and (b) the implementation of environmental enrichment to promote naturalistic behaviors. Both practices have their roots in behavior analysis, or the operant conditioning-centered, reward-based approach to behavioral psychology. Operant conditioning served as the foundation for the development of reinforcement-based training methods commonly used in zoos to make veterinary and husbandry procedures easier and safer for animals and their caregivers. Likewise, operant conditioning, with its focus on arranging environmental antecedents and consequences to change behavior, also provided a framework for successful environmental enrichment practices. In this paper, we outline the key individuals and events that shaped two of the cornerstones of the modern zoo: (1) the emergence of reward-based husbandry training practices, and (2) the engineering of environmental enrichment. In addition, we (3) suggest ways in which behavior analysis can continue to advance zoo welfare by (i) expanding the efficacy of environmental enrichment, (ii) using within-subject methodology, and (iii) improving animal-visitor interactions. Our goal is to provide a historical and contextual reference for future efforts to improve the well-being of zoo animals.