IM3 may refer to:
- Bristol Pegasus I.M3, a British aero engine
- Innocenti IM3, a BMC car model
- Onchan, Isle of Man (Royal Mail postcode
IM3) - Im3 (space group), a symmetry group; see List of space groups
- Indosat Multimedia Mobile (IM3), a telecommunications subsidiary
- Infamous Mobb (aka "IM3"), an American hip hop group
- Intermediate 3 (IM3), a competition class under British Rowing