The phosphoinositide 3-kinases (PI3-kinases) are a family of lipid kinases that have a key role in the regulation of many cellular processes including proliferation, survival, carbohydrate metabolism, and motility. There is now strong evidence that some members of the PI3-kinase family have an important role in cancer. Emerging evidence for functional specialisation of PI3-kinase isoforms suggests that isoform selective inhibitors, in contrast to the existing non-selective inhibitors wortmannin and LY294002, may prove to be useful anticancer drugs.