An increasing number of lead generation approaches are being applied to multi-target drug discovery (MTDD). Historically, focussed screening and a knowledge-based approach called framework combination have been most widely used â with varying degrees of success. More recently, alternative screening approaches such as HTS, fragment-based screening and in silico screening are being used alongside the traditional approaches in order to discover novel hits with attractive physicochemical and oral pharmacokinetic properties. Factors influencing the feasibility of discovering DMLs for particular combinations are discussed in this chapter. The role of natural products and the discovery of probes for chemical biology are also highlighted.