Equity Residential (EQR) is a real estate investment trust (REIT). The Company is focused on the acquisition, development and management of multi-family residential properties, which includes the generation of rental and other related income through the leasing of apartment units to residents, in United States. ERP Operating Limited Partnership (or Operating Partnership), which is an Illinois limited partnership, conducts the multifamily residential property business of EQR. All of the Company's property ownership, development and related business operations are conducted through the Operating Partnership. The Operating Partnership holds all of the assets of the Company, including the Company's ownership interests in its joint ventures. In December 2012, it acquired four multifamily properties totaling 1,134 units.