Meningiomas are among the most common primary tumors of the central neoplasm and are probably the most common primary nonglial tumor type. They are also the most common of the extra-axial tumors of the brain. Understanding of meningiomas and their classification, grading and molecular biology and genetics has evolved significantly over the past few decades. Environmental and genetic factors have been implicated in the development of these neoplasms. They arise from meningothelial (arachnoidal cap cells), typically situated in the meninges, near the dura. However, these cells can be found in other locations less commonly which accounts for the development of meningiomas in unusual locations (sometimes outside the central nervous system). Although the majority of these tumors are considered low grade neoplasms, classification and grading schemas have identified subtypes of meningiomas that are associated with more aggressive behavior or have unusual presentations. The fourteen chapters in this book address some of these various aspects of this diverse group of tumors.