A magnetic sail is a proposed method of spacecraft propulsion where an onboard magnetic field source interacts with a plasma wind to form an artificial magnetosphere that acts as a sail, transferring force from the wind to the spacecraft requiring little to no propellant as detailed for each proposed magnetic sail design in this article.

Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry.