1D, 1-D, or 1d can refer to:
- Alpha-1D adrenergic receptor
 - Astra 1D, a satellite
 - Canon EOS-1D, Canon's first professional digital camera
 - Long March 1D, a satellite
 - One-dimensional space in physics and mathematics
 - One Direction, an English-Irish boy band
 - Penny (British pre-decimal coin), routinely abbreviated 1d.
 1D, the hexadecimal code for the Group Separator control character
See also
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