This book is not a treatise on brain tumor pathology and nosography. It has been conceived as a help to pathologists, neuropathologists and neuro-oncologists in confronting everyday problems arising in the diagnostics of brain tumors. Today, because of scientific advances in clinical diagnosis brain tumors are operated earlier, when they are still of reduced dimensions, and with new techniques and more frequently they undergo biopsy procedures. As a consequence, surgical samples for diagnosis are of a smaller size. On the other hand, the recourse to therapies ever more selective require more and more precise identification of tumor types and grades and quite often reliance must be placed on a limited number of cells, as tumor morphological patterns are no longer available. The ever greater precision leads to an increased risk of a flawed diagnosis. The book aims to illustrate the pitfalls most frequently encountered today in the practical activity of diagnosis and also of prognosis. The initial chapters cover the distinction between infiltrating tumors and normal nervous tissue, between diffuse astrocytoma and oligodendroglioma and the identification of the malignant variant of some tumor types. Moreover, in the pathology of brain tumors, some biological processes are active which show a development over the course of time, such that in surgical samples they cannot be recognized as a whole, but only from the occurrence of limited and partial aspects. Invasion modalities, angiogenesis and apoptosis fall in this category and are discussed not in an exhaustive manner, but as stages or phases of the processes identified in the tissue. The figures do not seek to illustrate the characteristic aspects of the tumors, but only the points under discussion.This book is the result of many years of personal experience in the diagnosis of brain tumors as well as of discussions with neurosurgeons and neuro-oncologists and it aspires to contribute to solving emerging everyday problems.