The format of Essential Human Histology departs considerably from that of the usual presentations on human tissue/organ biology. This presentation was not designed as a formal reference textbook but as a tool solely for students and is designed for rapid student learning as well as rapid review in preparation for USMLE examinations. Essential Human Histology focuses the beginning student's attention on the most important aspects of this discipline which are presented as a series of learning units. In general, the text follows the traditional and logical sequence of cells to tissues to organs, but within this sequence, the discussion on mitosis is presented immediately after the cell and discussion on meiosis just prior to a consideration of the reproductive systems. To understand human structural biology, it is essential to learn a specialized vocabulary and to assimilate a large body of facts. Learning, as distinct from memorization, depends to a great degree on repetition and reinforcement and is made easier if the material to be learned can be presented in discrete, manageable segments. The format of Essential Human Histology is designed specifically to meet these requirements and, if used properly, will enable the student to master this knowledge quickly and efficiently. Use of this Textbook: The subject matter is broken down into small learning units, each of which is introduced by a vocabulary appropriate to that unit. The vocabulary introduces the main features of the subject to be discussed and provides the basic vocabulary for that unit. As each segment is read, note the vocabulary words (identified by bold print) in the text and how they contribute to the discussion. After completing the narrative segment, return to the vocabulary words, using them as prompts to recall the details of the material just read. The vocabulary serves as a summary of the topic and provides a means for rapid review. If a vocabulary word fails to prompt a response, it and the associated text can be found quickly from the bold type in the appropriate segment. A segment entitled either Histogenesis or Organogenesis provides an introduction into the development of each tissue and/or organ and provides another means of reinforcement that contributes to an overall understanding of the tissue or organ being considered. Summaries briefly outline the structural/functional relationships and serve to draw the information together and to provide an additional review of the topic. During preparation of Essential Human Histology, three major considerations were kept in mind: (1) most curricula place considerable time constraints on the student; (2) function and structure are inextricably related; and (3) the learning process essentially is a matter of repetition and reinforcement. The narrative strives to present the vast amount of information available on this topic, in a concise and logical manner, without sacrificing the detail that is necessary for a basic understanding of human tissue and organ biology.