The efficacy of traditional anti-cancer agents comes with the price of toxicity to normal cells, which limits the success of therapy. In the past 2 decades, greater understanding of the molecular differences between malignant and normal cells has led to the development of therapies that more specifically target human tumors. These include new anti-cancer agents directed against intracellular targets associated with malignant alterations, such as increased proliferation, impaired apoptosis or angiogenesis. In addition, antibodies have been developed that are directed towards tumor-associated antigens and provide tailor-made effector functions by inhibiting cell growth, inducing apoptosis or constituting cytotoxic drug delivery systems. Since the targeted approach of anti-cancer therapies increases the exposure of malignant cells and at the same time reduces the exposure of normal tissues, it offers the promise of enhanced efficacy and lower side effects. Antibodies, immunoconjugates and liposomal drug delivery systems derived thereof are now mainstream cancer therapeutics, and by the end of 2003 17 marketed antibody-based products generated several billion in combined annual sales. This study highlights the most recent breakthroughs in antibody technology and summarizes major achievements in antibody-based cancer therapy in oncology trials.