The insulin-like growth factor 1 receptor (IGF-1R) and its associated signalling system has provoked considerable interest over recent years as a novel therapeutic target in cancer. A brief outline of the IGF-1R signalling system and the rationale for its use in cancer medicine is given. This is followed by a discussion of the different possible targets within the IGF-1R system, and drugs developed to interact at each target. A systems-based approach is then used to review the in vitro and in vivo data in the published literature of the following compounds targeting IGF-1R components using specific examples: growth hormone releasing hormone antagonists (e.g. JV-1-38), growth hormone receptor antagonists (e.g. pegvisomant), IGF-1R antibodies (e.g. CP-751,871, AVE1642/EM164, IMC-A12, SCH-717454, BIIB022, AMG 479, MK-0646/h7C10), and IGF-1R tyrosine kinase inhibitors (e.g. BMS-536942, BMS-554417, NVPAEW541, NVP-ADW742, AG1024, potent quinolinyl-derived imidazo (1,5-a)pyrazine PQIP, picropodophyllin PPP, Nordihydroguaiaretic acid Insm-18/NDGA). The following tumour types are specifically discussed: lung, breast, colorectal, pancreatic, NETs, sarcoma, prostate, leukaemia, multiple myeloma. Other tumour types are mentioned briefly: squamous cell carcinoma of the head and neck, melanoma, glioblastoma, ovary, gastric and mesothelioma. Results of early stage clinical trials, involving recently patented drugs. are included where appropriate. We then outline the current understanding of toxicity related to IGF-1R targeted therapy, and finally outline areas for further research.