The Open Space Institute is a left-of-center environmentalist organization that seeks to prevent the development of land that is rich in natural resources. Open Space Institute does so by bundling contributions that allow the organization to purchase such properties with the intent of preventing their sale to individuals and businesses that plan to engage in land or energy development. 
The Open Space Institute was established in 1974. While originally created as a conservancy organization focused on the state of New York, today the organization is also active in New Jersey, South Carolina, and Florida. 
In 2019, the Open Space Institute received $3,761,533 in contributions, $3,908,202 in total revenue, and $2,465,419 in expenses.  At the end of the year, the Institute reported $6,443,582 in net assets. 
The organization conducts its purchases through a separate entity, the Open Space Institute Land Trust. In 2019, the Land Trust received $12,080,600 in contributions, $4,972,668 in program service revenue, $9,153,791 in investment income, and $27,628,155 in total revenue.  The same year, the Land Trust incurred $37,579,399 in expenses  and reported $245,848,911 in net assets. 
The Open Space Institute has purchased a variety of properties across the United States. The organization generally breaks down its purchase into five categories: land for recreation, land for clean water, land for habitat, land for healthy communities, and climate-related purchases. 
Most of the Open Space Institute’s purchases so far have been in New York. These include forest in the Beaver Kill Valley of the Catskill Mountains, the Manitou Nature Preserve, farmland in Saratoga County, the Palmerton Range and the Marion River Carry in the Adirondacks, 17,000 acres of land across the Hudson River Valley, and the Minnewaska State Park Preserve. 
In recent years, the Open Space Institute has made purchases in New Jersey, South Carolina, Vermont, and Florida. These include the Giralda Farms in New Jersey; 616 acres of land along Lake Champlain in Vermont, the 4,000-acre Triple Head Diamond Ranch in the Florida Everglades, and 259,000 acres of the Fairlawn Plantation in South Carolina. 
Christopher “Kim” J. Elliman is the president and CEO of the Open Space Institute.  Prior to joining the organization, Elliman was president of Gray Seifart Investment Management, a financial services firm. Prior to that, Elliman was a partner at the Elmrock Group, a private equity firm.