AER or Aer may refer to:

• AerCap, an aircraft lessor (NYSE stock symbol AER)
• Aer Lingus, airline from Ireland
• IATA airport code for Sochi International Airport in Krasnodar Krai, Russia

• Aerides, an orchid genus, abbreviated Aer
• Agranular endoplasmic reticulum, a cell organelle
• Albumin Excretion Rate
• Apical ectodermal ridge, critical component of vertebrate limb development

• Administrative expense ratio, a ratio of general and administrative expenses to total revenue
• Annual equivalent rate, a notational interest rate
• Average earnings ratio, in stocks

• Aer language, an Indo-Aryan language of Pakistan
• Eastern Arrernte language, an Arandic dialect cluster of Australia (ISO-639: aer)

• Aer (album), an album by Swiss pianist and composer Nik Bärtsch's band Mobile
• Aer (band), a hip-hop band

• Action For Economic Reforms, a public-interest research organization in the Philippines
• Advanced Engine Research, an endurance racing car engine manufacturer
• A.E.R. (automobile), a French former car manufacturer
• AER (motorcycles), a British motorcycle manufacturer
• Agri-Energy Roundtable, a non-governmental organization accredited by the United Nations
• Alberta Energy Regulator
• Algoma Eastern Railway, a former Canadian railway that operated in the province of Ontario
• Annual Equivalent Rate, as used in the UK
• Army Emergency Relief
• Assembly of European Regions, an independent network of European Regions
• Atmospheric and Environmental Research, an American scientific research agency owned by Verisk Analytics
• Australian Energy Regulator

• Aer (Sendai), a skyscraper in Japan

• All England Law Reports, covering the court system in England and Wales
• American Economic Review

• Aër, a liturgical item in the Greek Orthodox Church
• Air (classical element), in Greek mythology

• Address-Event Representation, a coordinate-based data format for sparse events in space-time.
• AER: Memories of Old, a 2017 adventure video game developed by Forgotten Key and published by Daedalic Entertainment
• All-electric range, the driving range of a vehicle using only electrical energy for propulsion