Pasteur put vaccination on an empiric and experimental basis during the 1880s, and vaccine development proceeded slowly until the second World War. During this period live vaccines against bacterial and viral diseases were developed by attenuation through passage in animals and killed microbes were inactivated without destroying their immunogenicity. Moreover, knowledge of bacterial toxins and polysaccharides permitted the development of new vaccines for several epidemic diseases. At the beginning of the third century of vaccination, classical methods are still providing new vaccines, but molecular biology and genetic engineering have begun to influence vaccine development. In addition, for the first time basic immunology is contributing to the domain of vaccinology. Thus, the current trends in vaccine development are as follows: reassortment of segmented genomes, attenuated strains recombined with genes from pathogens, vectors carrying foreign genes, replication-defective particles, DNA plasmids, and reverse vaccinology, among others. Also, new methods of vaccine delivery besides injection will be used and new adjuvants will be added to vaccines in order to stimulate specific responses. The future of vaccination is promising.