The review covers basic recent discoveries on the mechanism of action of adjuvants, which have been developed in the last decade. In particular, it focuses on the activation of TOLL like receptors and subsequent release of pro-inflammatory lymphokines (innate immunity), which, in turn, are thought to activate antigen specific responses (adaptive immunity). Given the number of novel adjuvants available to researchers, we limited the scope of the review to those adjuvants which are routinely used in our laboratories and of which we have first hand information.