The insulin-like growth factor (IGF) system is emerging as a promising new target in cancer therapy. Experimental models and epidemiological studies have demonstrated that the IGF system plays a key role in malignant transformation and cancer progression. Different strategies are being pursued to target this pathway. Several monoclonal antibodies and tyrosine kinase inhibitors targeting the IGF-1 receptor are in clinical development. Early clinical trials indicate these drugs have acceptable safety profiles, and there is pharmacodynamic evidence that actual target inhibition is achievable in patients. Emerging efficacy data as single agent and in combination with chemotherapy is encouraging yet too early for firm conclusions. This manuscript reviews the role of the IGF system in human malignancy and its interactions with other signaling pathways, and summarizes the available data of IGF-1R inhibitors currently in clinical trials.