Better catalysts are needed to address numerous challenges faced by humanity. In this Perspective, we review concepts and tools in theoretical and computational chemistry that can help to accelerate the rational design of homogeneous and heterogeneous catalysts. In particular, we focus on the following three topics: (1) identification of key intermediates and transition states in a reaction using the energetic span model, (2) disentanglement of factors influencing the relative stability of the key species using energy decomposition analysis and the activation strain model, and (3) discovery of new catalysts using volcano relationships. To facilitate wider use of these techniques across different areas, we illustrate their potentials and pitfalls when applied to the study of homogeneous and heterogeneous catalysts.