A variety of recombinant vaccines and vaccine delivery systems are currently under development as alternatives to vaccines produced in animals that are primarily administered by injections. These nonanimal alternatives do not transmit animal pathogens, are often rapid to develop, and can be produced on a large scale at low costs. Many of these new vaccine technologies are based on oral delivery systems and avoid the risks of disease transmission associated with the use of syringes for injectable vaccines. In addition, many of these novel systems have extended shelf life, often not requiring refrigeration and thus are applicable in developing countries or remote locations. Here we describe the development of microalgal-based immunization systems. Antigens expressed in the chloroplast or anchored to the surface of plasma membrane are shown to effectively immunize fish and rabbits. The effective oral delivery of antigens by microalgae provides a safe and inexpensive mechanism to immunize animals. The applications of microalgal vaccines are currently being investigated.