RK may stand for:
- Radial keratotomy
- Rajesh Khanna, a Bollywood film actor
- Reality Kings, a North American porn site
- Relient K, a Christian rock band
- Religious knowledge, also known as religious education
- Riddlin' Kids, a punk rock band from Austin, Texas
- Rikenium (Rk), a proposed name for Ununtrium
- Rilo Kiley, an indie rock band from Los Angeles, California
- Rizzle Kicks, an indie-rap duo from Brighton, UK
- r/K selection theory, relating to the trade-off between quantity and quality of offspring
- RK 95 TP or RK 62, Finnish assault rifles (RynnäkköKivääri)
- Royal Khmer Airlines' IATA airline designator