This textbook is based on the Biology of Parasitism course at the Marine Biological Laboratory in Woods Hole, Massachusetts, USA. For over 20 years, the course has offered a training ground for future generations of parasitologists. Its primary goal is to attract and introduce the best and most promising young researchers to the many unresolved problems in parasitology and prepare them for their future as independent investigators in the field. The rigorous syllabus combines laboratory research with a programme of visiting lecturers who bring together research in the field. The text is intended to present a snapshot of the content and spirit of the course. By presenting a series of chapters that reflect the formal lectures that students receive on a daily basis, as well as the approaches used during the laboratory section, the editors hope to share some of the science that occurs there. One part of the book presents the experimental component of the course, in particular the subject matter of the four two-week sessions covering immunology, biochemistry, cell biology and molecular biology of protozoan and helmith parasites. As in the course, the experimental part is complemented by a number of review-like chapters solicited from the large number of speakers who lecture during the course.