Since Russell and Burch (1959) suggested the principles of replacement, reduction, and refinement (3Rs) as a foundation for animal research, their influence has only grown in the research community. In this paper, we discuss whether the 3Rs can be constructively used as a prism to analyse decisions regarding the welfare of animals housed in zoos and aquariums (henceforth “zoo animals”). We analyse opportunities and challenges for each of the three Rs when applied to zoo animals. We discuss the following reasons (...) to consider the use of the 3Rs in relation to zoo animals: (1) there are similarities between motivations for housing animals in zoos and using them in research that are ethically relevant to consider; (2) the professional zoo community has committed to progress towards evidence-based best practice models to ensure and enhance the welfare of animals housed in zoos; and (3) there is a growing public concern regarding the welfare of zoo animals which can, to some extent, be met by viewing current practices through the prism of the 3Rs. (shrink)