We are a real estate investment trust, or REIT, that was organized under the laws of the State of Maryland in 1998. As of December 31, 2018, we owned 443 properties (469 buildings) located in 42 states and Washington, D.C. On that date, the undepreciated carrying value of our properties, which represents the gross book value of our real estate assets before depreciation and purchase price allocations, less impairment write downs, was $8.4 billion, excluding properties classified as held for sale. Our portfolio includes: 129 properties (155 buildings) leased to medical providers, medical related businesses, clinics and biotech laboratory tenants, or MOBs, with 12.6 million square feet of space and an undepreciated carrying value of $3.8 billion; 304 senior living communities, including independent living, assisted living, memory care and skilled nursing facilities, or SNFs, with 33,796 living units, with an undepreciated carrying value of $4.5 billion; and 10 wellness centers with approximately 812,000 square feet of interior space plus outdoor developed facilities with an undepreciated carrying value of $178.1 million.
Our principal executive offices are located at Two Newton Place, 255 Washington Street, Suite 300, Newton, Massachusetts 02458-1634, and our telephone number is (617) 796-8350.
We believe that the aging of the U.S. population will increase demand for existing MOBs, independent and assisted senior living communities, SNFs, wellness centers and other medical and healthcare related properties. We plan to profit from this demand by acquiring additional properties and entering into leases and management arrangements with qualified tenants and managers which generate returns to us that exceed our operating and capital costs, including structuring leases that provide for or permit periodic rent increases.