More than fifty years after its initial discovery by Rita Levi Montalcini and Stanley Cohen and the proposal of the neurotrophic theory, nerve growth factor (NGF) has become the prototype of a family of biologically active molecules called neurotrophic factors (NTFs). This book addresses important advances in NTF research, from basic science to clinical medicine. It focuses mainly on NGF, but also includes individual chapters dealing with the brain-derived neurotrophic factor (BDNF) and ligands of the glial cell line-derived neurotrophic factor (GDNF) family, which have attracted increasing interest in the neuroscience community because of their diverse effects in the normal and diseased brain. In the first part of the book, the authors provide the necessary background for the following chapters and discuss the basic mechanisms and pathways of NGF signal transduction.