A "first surface" mirror or front surface mirror (also commonly abbreviated FS mirror) is a mirror with the reflective surface being above a backing, as opposed to the conventional, second surface mirror with the reflective surface behind a transparent substrate such as glass or acrylic.

They are made for applications requiring a strict reflection without a ghosting effect as seen with a second surface mirror - where a faint secondary reflection could be observed, coming from the front surface of the glass. This includes most optics applications where light is being manipulated in a specific manner. Telescopes, rear projection televisions, periscopes, and high quality kaleidoscopes use this type of mirror.