Newtonian refers to the work of Isaac Newton, in particular:
- Newtonian mechanics, also known as classical mechanics
- Newtonian telescope, a type of reflecting telescope
- Newtonian cosmology
- Newtonian dynamics
- Newtonianism, the philosophical principle of applying Newton's methods in a variety of fields
- Newtonian fluid, a fluid that flows like water—its shear stress is linearly proportional to the velocity gradient in the direction perpendicular to the plane of shear
- Non-Newtonian fluids, in which the viscosity changes with the applied shear force