The general aspects of symbiosis with specific reference to the costs/benefits trade off between the two partners, the importance of symbiosis as a source of evolutionary innovation, the different types of association (intracellular-, photosynthetic- and intestinal symbioses) and the Serial Endosymbiotic Theory will be briefly discussed in the first three lessons of the course. The producers/scroungers relationships, the morphological, trophic and reproductive adaptations of parasites, parasite-host coexistence and coevolution strategies will be approached in three lessons more. The remaining ten lessons will be used to take into consideration the most common human and animal parasites analyzing their life cycles, geographic distribution, epidemiology, and pathogenicity.