Macrophages are multi-functional immune cells with key roles in host defense and tissue remodelling. The broad array of macrophage functions has prompted the development of very diverse smart fluorescent architectures, rationally designed to elicit a fluorescent signal only after target engagement. This tutorial review covers recent advances in the design, synthesis and application of smart fluorescent probes for imaging macrophage cellular activity, ranging from small fluorophores to peptide-based probes with internally quenched fluorescent pairs or activity-based reactive groups.