The complement system is a part of the immune system which improves the capability of phagocytic cells and antibodies to take out damaged cells and microbes from the organism's body. Complement control proteins, which are found in a higher concentration in the blood plasma as compared to complement proteins, regulate the complement system. Some of the complement control proteins are found on the membranes of self-cells that protect them from attack by the complement system. This system is considered to be focused on killing bacteria that infect the host organism. Furthermore, it acts as an innate immune surveillance system, which has a significant role to play in host homeostasis, defense against pathogens and inflammation. The dysfunction of the complement system is a major reason of diseases caused in the central nervous system, such as neurodegenerative conditions like spinal cord injuries and Alzheimer's disease. C3 glomerulopathy and atypical hemolytic uremic syndrome have been found linked with mutations in the genes of complement regulators specifically factor H. The readers would gain knowledge that would broaden their perspective about the complement system and its immunobiology through this book. It will help the readers in keeping pace with the rapid changes in this area of study.