Understanding blood flow in the circulatory system has attracted scientific interest for several centuries, with perhaps the most notable early work being the 1628 publication of An Anatomical Study of the Motion of the Heart and of the Blood in Animals by William Harvey. However, due to technical difficulties in conducting appropriate experiments in the vasculature of living organisms, blood flow studies until early in the twentieth century were mostly based on observations in cylindrical tubes. Therefore, observations on blood flow in narrow tubes have provided the majority of basic information on blood flow dynamics, including the influence of red blood cell (RBC) properties. These early studies on blood flow in cylindrical tubes are briefly summarized in this chapter, with more detailed information available elsewhere (Goldsmith et al. 1989).