Cellular analysis in hematology has a fascinating history, spanning more than three centuries. This chapter summarizes that history. Cell analysis began with the first observation of blood cells through a simple microscope by Jan Swammerdam in 1668, although the first publication was by van Leeuwenhoek in 1675. They and those who followed them made many important observations using microscopes. Paul Ehrlich brought a new dimension to microscopic observation by applying stains to blood cells in 1877. Manual cell counting methods using microscopes have to a large extent been replaced by automated methods that have improved the quality as well as efficiency of analysis. Automated cell counters began by counting and sizing red cells, white cells, and platelets. Improved technology for counting and analysis, together with the addition of some features of flow cytometers, have progressively added the white cell differential count, reticulocytes, nucleated red cells, and abnormal cells to the capabilities of modern multiparameter hematology analyzers.