Activity-based protein profiling (ABPP) has emerged as a powerful strategy to study the activity of enzymes in complex proteomes. The aim of ABPP is to selectively visualize only the active forms of particular enzymes using chemical probes termed activity-based probes (ABPs). These probes are directed to the active site of a particular target protein (or protein family) where they react in a mechanism-based manner with an active site residue. This results in the selective labeling of only the catalytically active form of the enzyme, usually in a covalent manner. Besides the monitoring of a specific enzymatic activity, ABPP strategies have also been used to identify and characterize (unknown) protein functions, to study up- and down-regulation of enzymatic activity in various disease states, to discover and evaluate putative new enzyme inhibitors, and to identify the protein targets of covalently binding natural products. In this Topical Review we will provide a brief overview of some of the recent developments in the field of ABPP.