RER

RER may refer to:

In France

 * Réseau Express Régional, or RER d'Île-de-France, the commuter rail service serving Paris and its suburbs
 * Réseau Express Régional Franco-Valdo-Genevois, now called Léman Express, commuter rail service serving Geneva (Switzerland), Annemasse (France) and its suburbs

In Belgium

 * Réseau express régional Bruxellois ('Brussels Regional Express Network'), the commuter rail service serving Brussels and its suburbs and commuters
 * Réseau Express Régional Gantois ('Ghent Regional Express Network'), the commuter rail service serving Ghent and its suburbs and commuters

In Switzerland

 * Réseau Express Régional Bernois, the name used for the Bern S-Bahn in French speaking areas.
 * Réseau Express Régional Vaudois, commuter rail service serving Vaud and its suburbs
 * Réseau Express Régional Fribourgeois, commuter rail service serving Fribourg and its suburbs
 * Réseau Express Régional trinational de Bâle, the name used for the Basel S-Bahn in French speaking areas.
 * Réseau Express Régional franco-valdo-genevois, now called Léman Express, commuter rail service serving Geneva, Annemasse and its suburbs

In Argentina

 * Red de Expresos Regionales, a planned commuter rail service in Buenos Aires

In Canada

 * GO Regional Express Rail, now known as GO Expansion, a planned commuter rail service in Toronto and its suburbs

Other uses

 * Rebuilt Reading electric multiple units
 * 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