RER may refer to:

Transport

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, 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

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