The human skin, as the largest organ of the body, is home to numerous neoplastic and non-neoplastic disorders. The vast majority of non-neoplastic skin diseases are inflammatory in nature, while a small subset is non-inflammatory. This book covers 194 non-neoplastic dermatologic conditions, classified by their primary microscopic tissue reaction patterns. Our aim is to provide a concise, practical, and up-to-date review of these diseases. We offer a discussion on the clinical presentation, histopathologic features, pathogenesis, differential diagnosis, and management for each entity. One of the key attributes of this clinical atlas is the abundant collection of clinical and microscopic images used to illustrate the salient features of these disorders. In this book, we will focus on inflammatory dermatoses, which encompass a wide range of dermatologic conditions that can be challenging to diagnose due to significant overlaps in clinical and histopathologic features. Dermatopathologists are more likely to encounter unusual or ambiguous cases that are particularly difficult to classify. The interpretation of non-neoplastic skin biopsies requires not only microscopic pattern recognition but also careful integration of clinical history, laboratory data, and other ancillary findings, wherever available, to render the most appropriate diagnoses. We hope that this book will help our readers as they interpret challenging skin biopsies for non-neoplastic diagnoses.