Metal complexes are increasingly being used to inhibit enzymes. The reasons for this increased interest arise from the special features that metal complexes offer, e.g. the facile construction of 3D architectures that tightly fill enzyme active sites increasing selectivity and the possibility of facile coordination to protein residues that enhances enzyme inhibition. In this review we classify the main modes of enzyme inhibition by metal-based complexes and correlate the enzyme inhibition activity to macroscopic properties such as anticancer activity.