Inducing adaptive immune responses with vaccination requires prior innate immune responses. Adjuvants have been used empirically to enhance and modulate the adaptive immune responses elicited by the vaccination. Advances in the innate immune system revealed that many adjuvants act through the innate immune receptors including TLRs, NLRs, RLRs, and CLRs. Recently it has been shown that some particulate adjuvants directly activate dendritic cells in a receptor-independent manner. In this review, we discuss how adjuvants activate dendritic cells, directing adaptive immune responses to Th1, Th2, and Th17 cells. We also discuss a differential requirement of adjvuant between priming and boosting administration of vaccine, and appropriate use of adjuvants to reduce the side effect of vaccine.