Over the past few decades, category theory has come to be seen as a valuable technique in providing semantics for idealised programming languages, clarifying central features of languages used in practice. For instance, category theory has been used to study domain equations and model recursion in both programs and types, to study parametric phenomena as appear in many languages in various guises, and to give a unified study of computational effects. In this session, our three speakers, John Power, Neil Ghani, and Stefan Milius, explain in depth three particular ways in which category theory has been and continues to be used to model programming features. In doing so, they focus on the underlying mathematics that supports their analysis, with an eye towards seeing the connections between the programming features and seeing semantically how they might be combined.