This is a translation of Edward Purcell's famous lecture notes "Life at low Reynolds number," published in the AIP Conference Proceedings. The original text was presented at a symposium in honor of Victor Weisskopf and later published in the American Journal of Physics. The lecture discusses the unique challenges and behaviors of organisms operating in low Reynolds number environments, where viscous forces dominate over inertial forces. It highlights the importance of understanding fluid dynamics at microscopic scales, where the Reynolds number is typically very small. The lecture emphasizes that in such environments, movement is not driven by inertia but by the forces exerted by the fluid. It also discusses the role of viscosity, the difficulty of propulsion in such conditions, and the unique swimming mechanisms of microorganisms like bacteria. The lecture concludes by explaining how even small organisms can navigate their environment efficiently, despite the challenges posed by low Reynolds numbers. It also touches on the importance of diffusion and the limitations of stirring in such environments. The lecture provides a comprehensive overview of the physics of low Reynolds number systems, emphasizing the need for a different approach to understanding fluid dynamics at microscopic scales.This is a translation of Edward Purcell's famous lecture notes "Life at low Reynolds number," published in the AIP Conference Proceedings. The original text was presented at a symposium in honor of Victor Weisskopf and later published in the American Journal of Physics. The lecture discusses the unique challenges and behaviors of organisms operating in low Reynolds number environments, where viscous forces dominate over inertial forces. It highlights the importance of understanding fluid dynamics at microscopic scales, where the Reynolds number is typically very small. The lecture emphasizes that in such environments, movement is not driven by inertia but by the forces exerted by the fluid. It also discusses the role of viscosity, the difficulty of propulsion in such conditions, and the unique swimming mechanisms of microorganisms like bacteria. The lecture concludes by explaining how even small organisms can navigate their environment efficiently, despite the challenges posed by low Reynolds numbers. It also touches on the importance of diffusion and the limitations of stirring in such environments. The lecture provides a comprehensive overview of the physics of low Reynolds number systems, emphasizing the need for a different approach to understanding fluid dynamics at microscopic scales.