The complement system, a vital component of innate immunity, is indispensable to our immune defence mechanisms against microbial infections. Acting as a surveillance mechanism, it identifies and eliminates pathogens by activating several complement components and associated signalling pathways, which are also implicated in various diseases and disorders. Beyond its defensive role, the complement system has emerged as a promising target for vaccine development in therapeutic and preventive regimens, offering new vaccine strategies to combat non-infectious and infectious diseases. Activation of the complement pathways by various natural and synthetic adjuvants enhances protective immune responses, highlighting its utility in vaccine design. This approach could be useful for targeting autoimmune diseases, infectious diseases, cancer and neurological disorders.