Laminar flow describes the most orderly regime of a fluid in motion, where laminar layers of a fluid slide parallel to the direction of the flow. Under these conditions, the lateral mixing is very low and the diffusion transport becomes an important factor. The Reynolds number is the key parameter for fluid dynamics studies, enabling the discrimination between laminar and turbulent flows. Blood in a capillary and reagents in a microfluidic device are both examples mainly characterized as laminar flows. The study of laminar flows leads to further understanding the human microcirculation and could induce technological advances in the manipulation of the fluids at the micro-meter scale.