In mathematics, physics, and art, moiré patterns (UK: MWAR-ay, US: mwar-AY, French: [mwaʁe] (listen)) or moiré fringes are large-scale interference patterns that can be produced when a partially opaque ruled pattern with transparent gaps is overlaid on another similar pattern. For the moiré interference pattern to appear, the two patterns must not be completely identical, but rather displaced, rotated, or have slightly different pitch.

Moiré patterns appear in many situations. In printing, the printed pattern of dots can interfere with the image. In television and digital photography, a pattern on an object being photographed can interfere with the shape of the light sensors to generate unwanted artifacts. They are also sometimes created deliberately – in micrometers they are used to amplify the effects of very small movements.

In physics, its manifestation is wave interference such as that seen in the double-slit experiment and the beat phenomenon in acoustics.