This atlas, which portrays the morphologic characteristics of normal and pathologic cells in blood and bone marrow, is published for the use of medical students, student medical technologists, and other health science students who are learning to identify the various types of blood cells. This monograph also is an aid for teachers of morphological hematology and for technologists who are responsible for the examination of smears by manual and automated methods. A knowledge of morphology is also useful for residents in clinical and anatomic pathology, pediatrics, and medicine. Major emphasis is placed on the anatomical characteristics of individual cells in the various stages of their maturation as revealed by light microscopy, employing an oil-immersion objective. Unless otherwise stated, the cells that are described and visually pictured by the artist, Dorothy Sturm, are those present in thin, air-exposed, dried smears or marrow imprints that have been stained by Wright stain.