The White House grounds consist of 18 acres located within the larger 55-acre area known as President’s Park (it also encompasses the Ellipse, Lafayette park, the White House Visitor Center, and the Grounds of the Executive Office Building). Twelve agencies and organizations share some portion of responsibility for the White House, according to Bradley H. Patterson, the author of the White House Staff: Inside the West Wing and Beyond. But the primary duties fall to the White House Liaison Office at the National Park Service (about 25 employees), the White House Center Service Delivery Team at the General Services Administration and the residence staff at the White House.