Targeted alpha therapy is an advancing experimental therapy that holds promise to deliver high cytotoxicity to targeted cancer cells. Initially thought to be indicated for leukaemia and micrometastases, there is now evidence that solid tumours can also be regressed. Alpha therapy may be molecular or physiological in its targeting. Alpha emitting radioisotopes such as Bi-212, Bi-213, At-211 and Ac-225 are used to label monoclonal antibodies or proteins that target specific cancer cells. Alternatively, radium-233 is used for palliative therapy of breast and prostate cancers as it is a bone seeking element. Progress in the development of clinical trials of alpha therapy is examined for leukaemia, lymphoma, melanoma, glioblastoma multiforme, bone metastases, ovarian cancer, pancreatic cancer and other cancers. Results of past and current trials are reviewed, and the bases of some proposed trials are presented.