Internal medicine residents face a wide range of challenging medical conditions during their training and need to be equipped with both the knowledge and flexibility to handle whatever comes their way. As part of a collaborative initiative, we present the Medical City Arlington Internal Medicine Handbook, a practical resource built by residents, for residents. This handbook brings together practical insights, evidence-based practices, and specialized clinical expertise, all with the goal of enhancing the diagnostic and treatment skills of internal medicine practitioners. It covers a broad spectrum of conditions, from common ailments to rare and complex diseases, and provides in-depth management strategies, treatment guidelines, and diagnostic tools. The handbook is organized into sections covering key areas like cardiology, pulmonology, gastroenterology, endocrinology, infectious diseases, and rheumatology, with each chapter providing concise, evidence-backed recommendations. What makes this handbook special is its collaborative nature. Residents from multiple hospitals contributed their knowledge and experiences, creating a resource that not only helps residents expand their own expertise but also gives them a chance to be part of something that will guide future residents. In today’s fast-moving healthcare environment, where medical conditions are becoming increasingly complex, this handbook is designed to help residents make faster, more accurate clinical decisions. Ultimately, this collaborative effort strives to foster a culture of continuous learning, teamwork, and excellence in patient care.