The purpose of the ORNL Fusion Power Demonstration Study (Demo study) is to develop a plan for demonstrating, in this century, the commercial feasibility of fusion power based on the tokamak concept. The two-year study was initiated in FY 1976, and this interim report summarizes the results for FY 1976. Major results include: (1) the outline of a three-phase plan for demonstrating the commercial feasibility of tokamak fusion power in this century; (2) a parametric analysis of tokamak costs which provides the economic basis for the demonstration plan; and (3) a critical evaluation of the technological directions, design approaches, and plasma characteristics which serve as the technical basis for the demonstration plan.