The general features and coordination chemistry of Os are discussed in the context of the use of different ligand types to stabilize complexes of Os
VIII
through to Os
−II
. The complexation chemistry with cyanide, N‐, P‐, O‐, S‐, and halide‐donor ligands is detailed. The asymmetric dihydroxylation and aminohydroxylation of alkenes, general coordination chemistry with macrocyclic and open chain ligands, porphyrin complexes, photophysical properties and electrochemistry of Os
II
complexes of heterocyclic ligands and comparisons to their Ru
II
analogues, and electron transfer in heterobimetallic and dendrimer complexes of Os
II
are all highlighted.