There are two types of immunity. innate and Acquired. Innate immunity is the immunity that is present since birth. It is very different from Acquired immunity as it is nonspecific. Acquired immunity is also known as Adaptive immunity. It is very specific and thus can differentiate between self and non self. Another main difference between Innate and Acquired is that Acquired immunity not only protects the body from infections but also prepares the body for further attack. This is due to the formation of memory cells. Acquired immunity is again of two types: AMI (Antibody mediated immunity) and CMI (Cell mediated immunity). Immunity can also be classified as Active and Passive. Active immunity is the introduction of Antigens which induces formation of Antibodies and this can be done Naturally or Artificially. Artificially it is done by use of Vaccines. Vaccines are live or attenuated pathogens which trigger the memory cells and also formation of Antibodies. But the main principle is to retain memory.