&NA;The bone marrow is a complex organ, with dynamic hematopoietic and immunologic functions. Disseminated within the intertrabecular and medullary spaces of the bones, it is estimated to be the same size as the liver. Because diagnostic samples are small representations of the total marrow, it is important that material be adequate, representative, and of high technical quality. A preview of the clinical profile, the complete blood count, and the peripheral blood smear will ensure that a minimum of additional ancillary testing is necessary to establish a diagnosis in these times of cost containment. Whereas newer technologies have enriched our understanding of pathogenesis and simplified cellular identification, it is important not to abandon the central role of light microscopy. Presented herein is a general review of bone marrow examination; indications for the same; logistics of procurement; a breakdown of procedures ideally suited for specimen components; and guidelines for interpretation and data integration according to cell line, tissue compartment, and pathogenic process.