Equity Residential, a Maryland real estate investment trust formed in March 1993, is an S&P 500 company. The Company is engaged in the acquisition, development and management of apartment properties in U.S. growth markets. It owns and manages nearly 400 properties located in Boston, New York, Washington, DC, South Florida, Seattle, San Francisco, Southern California and Denver. ERP Operating Limited Partnership (ERPOP), an Illinois limited partnership, was formed in May 1993 to conduct the multifamily residential property business of the company. The Company is the general partner of, and as of December 31, 2014 owns 96.2% ownership interest in, ERPOP. All of the Company's property ownership, development and related business operations are conducted through the Operating Partnership and the company has no material assets or liabilities other than its investment in ERPOP. The Company's corporate headquarters are located in Chicago, Illinois and the Company also operates property management offices in each of its markets. The Company, directly or indirectly through investments in title holding entities, owns all or a portion of 391 properties located in 12 states and the District of Columbia consisting of 109,225 apartment units. The Company The Company competes with other entities that have greater resources than the Company and whose managers have more experience than the Company's managers. Federal, state and local laws and regulations relating to the protection of the environment may require a current or previous owner or operator of real estate to investigate and clean up hazardous or toxic substances or petroleum product releases at such property.