This e-book, Topics on the Pathology of Protozoan and Invasive Arthropod Diseases, was originally conceived as a companion volume of our earlier book, Pathology of Infectious Diseases, Helminthiases, published in the year 2000. During the production of the current volume, however, administrative circumstances were not conducive to its publication as a hardcover book. We are pleased nevertheless to be able to present this treatise on protozoan and invasive arthropod related diseases electronically. As such, a great advantage is that it will be available freely to a wider audience; not just to the so-called developed world, but to less affluent and more remote areas-- in fact to anyone with access to the internet worldwide. This publication comes at an appropriate time when there is ever increasing attention being given to the neglected tropical diseases of this world, and as world travel is increasing. Pathologists highly experienced in many of the diseases discussed here are often not locally available, increasing the likelihood that accurate diagnoses will be unduly delayed.