RGA may refer to:
- Royal Garrison Artillery, a pre-1930 corps of the British Army,
- Republican Governors Association, an association for governors in the United States who belong to the United States Republican Party
- Red-Green Alliance (Denmark), a far left-wing political party in Denmark
- Residual gas analyzer, a small mass spectrometer
- Reallexikon der germanischen Altertumskunde. a German-language encyclopedia of the history of the Germanic peoples
- Reinsurance Group of America, a reinsurance company
- Restricted Growth Association, a UK charity that supports people with dwarfism
- Relative Gain Array, a tool to determine optimal input-output parings for MIMO systems