Homo- and heterocycles containing transition-metal-functionalized phosphorus atoms are at the interface between organometallic and main group chemistry. In contrast to the familiar phosphane-metal complexes, where the organophosphane acts as good donor ligand with moderate acceptor properties, in metal-functionalized phosphanes the complex metal fragment transfers electron density onto the phosphane fragment enhancing its basicity. The compounds under discussion merit special interest, as they not only possess the features of either component but also exert unique properties. They are available by a number of synthetic approaches. Most prominent routes make use of the nucleophilic displacement of halide by carbonyl metalates and of cyclocondensation and cycloaddition processes.