The book reports on the research findings of an investigation of two Kenyan plants namely Asparagus setaceous and Caesalpinia volkensii which were investigated on their antimicrobial and immunomodulatory properties. Several extracts from these plants were found to possess antimicrobial activities against selected pathogens. In addition, most of the extracts were found to be able to alter the functions of the immune system and immune cells. The results therefore scientifically verify and validate the usage of these plants in the treatment of infectious diseases. It further lend credence to the fact that the main mechanism of action of these plant extracts in fighting infectious diseases is through modulation of the immune system and cells. This is not to say that antimicrobial activity may not be playing a role but in vivo studies may be required to establish the extent of their role in treatment of these diseases.