This book addresses the current concepts in tissue acquisition, diagnosis, and classification of mediastinal lesions in small biopsies including cytology. Examples of mediastinal diseases that are either more common, more challenging to diagnose, or have a differential diagnosis that is important and might require different modes of treatment are highlighted. The knowledge of some key morphologic features and immunohistochemical pitfalls will be helpful for the practicing pathologist to tackle this challenge. The general workup of a mediastinal biopsy and the workup of major disease groups in mediastinal pathology which the general pathologist should be familiar with is discussed. Morphologic and, if applicable, immunophenotypic and molecular features that can help to distinguish these disease entities are highlighted. Furthermore, the reader will learn about the pertinent clinical implications of the diseases. Mediastinal Lesions: Diagnostic Pearls for Interpretation of Small Biopsies and Cytology will be a reference guide for pathologists, pathologists-in-training, and allied professionals, including oncologists, pulmonologists, surgeons, and radiologists.