Explore spin circuits in this 21-minute lecture from the nanoHUB-U course "Fundamentals of Nanoelectronics Part B: Quantum Transport" taught by Supriyo Datta. Delve into advanced concepts of quantum transport as they relate to spin-based electronic circuits, building upon the foundational understanding of how current flows at the atomic scale in nanotransistors. Learn how spin properties of electrons can be utilized in circuit design and understand the quantum mechanical principles governing spin transport phenomena. Examine the theoretical framework connecting spin dynamics to practical electronic applications, particularly relevant for understanding modern nanotechnology where devices operate with active regions spanning only a few hundred atoms. Gain insights into non-equilibrium statistical mechanics concepts that apply to spin-dependent transport processes, suitable for students and professionals in science and engineering fields with background in linear algebra and differential equations.