RPN may refer to:

Mathematics
Reverse Polish notation, a.k.a. postfix notation, a mathematical notation
 real projective space

Nursing
Registered practical nurse
Registered psychiatric nurse

Other uses
Radio Philippines Network, Channel 9
 (National Housing Programme), public housing in Brunei
Recherche en Prévision Numérique, weather forecasting researcher, Canada
Registered Parameter Number, in MIDI
Risk Priority Number, in failure analysis
Rosh Pina Airport (IATA code), Israel