One-way or one way may refer to:

• One-way traffic, a street either facilitating only one-way traffic, or designed to direct vehicles to move in one direction
• One-way function, a function that is easy to compute on every input, but hard to invert given the image of a random input
• One-way encryption
• One-way mirror, a glass through which one can see only in one way

One-Way is a 1994 novel by the French writer Didier Van Cauwelaert. It received the Prix Goncourt. It was adapted into the 2001 film Un aller simple, directed by Laurent Heynemann.