When we began to review the biochemistry and genetics material covered in the USMLE Step 1 at the end of our second year at Yale Medical School, we realized that most of the practice questions were approaching the material from a clinical perspective and not from the basic science perspective in which we had learned these topics. Although we had taken introductory biochemistry and genetics courses back in college and covered the material again during the first few months of medical school, we found ourselves studying the clinical aspects of biochemical and genetic diseases for the first time. Flipping through the highly rated biochemistry and genetics review sources, we realized that there was no gold standard review source for these high-yield topics that make up 15% of USMLE Step 1 questions.Lange^® Flashcards: Biochemistry & Genetics is the result of our struggles in studying these topics for Step 1 with the clinical slant that the boards demand. These cards offer the most complete, concise, and high-yield information for the major biochemical and genetic diseases tested on Step 1 and in medical school basic science courses. We are confident that the content covered in the third version of our cards includes the most current and board-relevant information that cannot be found in any other single biochemistry and genetics review text. We added a current medical student editor to help ensure that the content is up-to-date and boards relevant.We are pleased to present this information in a format modeled after Lange^® Flashcards: Pathology, our first publication in this series. Each card provides a structured presentation of a specific disease and allows students to easily compare and contrast diseases. The introductory cards in each chapter describe the basic principles of biochemistry and genetics that are board relevant and high yield. Each disease-specific card contains a clinical vignette on one side and important characteristics on the reverse side. These characteristics are organized into sections entitled biochemical or genetic defect, pathophysiology, clinical manifestations, treatment, and additional pearls. The most salient features of each disease are highlighted in bold for ease of rapid review.We suggest using these cards as an adjunct to your biochemistry and genetics courses in medical school. Being familiar with these cards early on will be very helpful during your Step 1 review. We also encourage you to jot down your own notes in the margins and to make these cards your personal biochemistry and genetics review for the boards.We are confident that the newly revised third edition of Lange^® Flashcards: Biochemistry & Genetics will be one of the most powerful tools to help prepare you for the boards and will serve as a resource that will bridge your basic science knowledge with the clinical aspects of disease. We wish you the best of luck on Step 1 and welcome your comments on how to improve this study tool in the next edition.