Combinatorial chemistry in combination with high-throughput screening technologies is an important way of finding new successful catalyst systems. The design of ligand libraries of bidentate phosphorus ligands and the application of their transition-metal complexes in homogeneous (asymmetric) catalysis reactions will be described in this review. Till now three different approaches were developed to arrive at such libraries of bidentate phosphorus ligands: 1) modular synthesis of bidentate ligands 2) the solid support synthesis of bidentate ligands and 3) the self-assembly of ligand building blocks into bidentate ligands. The scope and limitations of these strategies will be discussed on the basis of a limited number of articles that dealt with the synthesis of at least 15 bidentate phosphorus ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)