While a complete blood count provides information regarding possible treatment-related effects reflected in the peripheral blood, morphological evaluation of bone marrow cytology and paraffin sections provides information about bone marrow tissue architecture that otherwise would be missed by examination of peripheral blood alone. In decalcified, paraffin-embedded, hematoxylin and eosin (H&E)-stained sections of bone marrow, the more mature stages of the erythroid and myeloid cells, adipocytes, mast cells, and megakaryocytes can be identified, but lymphoid cells as well as immature progenitor cells can not be reliably identified. The quality of the marrow sections is governed by numerous variables related to specimen collection and processing and must be considered. In addition to discussing normal structure, function, and histology of bone marrow, methods for preparation and evaluation of bone marrow are presented.