RER

RER may refer to:

Transport

 * Brussels Regional Express Network (Réseau Express Régional), the commuter rail service serving Brussels and its suburbs and commuters
 * GO Regional Express Rail, a planned commuter rail service in Toronto and its suburbs
 * Rebuilt reading electric multiple units
 * Red de Expresos Regionales, a planned commuter rail service in Buenos Aires
 * Réseau Express Régional, the commuter rail service serving Paris and its suburbs
 * Rhône Express Régional, a commuter rail service between Geneva and Bellegarde-sur-Valserine

Other uses

 * The Real Estate Roundtable, a non-profit public policy organization that represents the interests of real estate
 * Real exchange rate, the purchasing power of a currency relative to another at current exchange rates and prices
 * RēR, the standard abbreviation for the label Recommended Records
 * Resident Evil: Revelations, a Capcom game
 * Respiratory exchange ratio, the ratio between the amount of carbon dioxide produced in metabolism and oxygen used
 * Rough endoplasmic reticulum, a type of endoplasmic reticulum protein-manufacturing ribosomes