Abnormalities in the Wnt signalling pathway are found in a wide range of cancers. The diverse origin of these malignancies implies that the contribution that disrupted Wnt signalling makes to tumourigenesis is not limited to specific tissue types and thus can be regarded as a step which is 'generic' to the process of carcinogenesis. In recent years, rapid progress has been made in the understanding of the Wnt signalling pathway, giving an insight into how inappropriate activation of this pathway may facilitate the neoplastic conversion of a normal cell. Furthermore, elucidation of the mechanisms that regulate Wnt signalling has led to the possibility of manipulating these mechanisms in order to down-regulate Wnt signalling in established tumours. In this review, the Wnt signalling pathway is described. The role of aberrant Wnt signalling in tumour development is discussed together with its clinical implications for anti-tumour therapy.