The inverse correlation between allergic diseases and helminth infections has been debated for over 30 years. It was initially assumed that the underlying mechanism is an imbalance between Th1 and Th2 responses that, as a result of reduced exposure to Th1-inducing infectious pathogens, has tipped to allergic Th2 responses. It has only recently been clearly demonstrated that helminth infections have negative effects on allergic disease manifestation. This was shown to be consistent with the activity of regulatory cell populations, which control the effector mechanisms of both Th1 and Th2. In this book, international experts in the field discuss the various roles of the cell populations involved in allergic reactions and helminth infections such as regulatory T and B cells, natural killer T cells, mast cells and basophils. Essential for specialists and students in the field, the contributions to this volume pave the way to new directions of research for the successful immunization against helminths and the prevention of inflammatory responses in allergic and autoimmune diseases.