[en] Significant progress was made during the past year in carrying out theoretical investigations pursuant to the scientific mission of the Institute. These achievements may be approximately classified in terms of the following categories (often with considerable overlap): sawteeth and MHD studies, turbulence theory and plasma transport, computational plasma physics, stability theory, mathematical physics, advanced ideas, and space plasma physics-related problems. An overview of this work is contained in this report. Detailed summaries of IFS Reports written during FY 89 are given in abstract form