Expander can refer to:
Part of the process of audio level compression
Part of the process of signal compression
Part of the process of companding
MIDI processor, hardware or software, to synthesize sounds from MIDI commands
Turboexpander, a turbine for high-pressure gas
Expander graph, a sparse graph used in the combinatorics branch of mathematics
StuffIt Expander, a file decompressor software utility
"Expander", a song on the album Accelerator by The Future Sound of London
Orthodontic expander, a device to widen the upper jaw