ISCOMs are typically 40 nm cage-like structures comprising antigen, saponin, cholesterol and phospholipid. ISCOMs have been shown to induce antibody responses and activate T helper cells and cytolytic T lymphocytes in a number of animal species, including non-human primates. Recent clinical studies have demonstrated that ISCOMs are also able to induce antibody and cellular immune responses in humans. This review describes the current understanding of the ability of ISCOMs to induce immune responses and the mechanisms underlying this property. Recent progress in the characterisation and manufacture of ISCOMs will also be discussed.