This paper addresses analysis and analysis practices for defense planning and their implications for modeling and simulation (M & S). The analysis in question is accomplished for Quadrennial Reviews and for continuing work on capability assessments, requirements analysis, and program analysis. The paper's purpose is to delineate priorities for the way ahead i.e., for investments and other actions to ensure that future M & S will serve the needs of defense planning analysis. Traditionally, analysis for defense planning has been at the strategic and operational levels, but what these levels now include is unclear, given that the organization of forces is changing, low-level activities can have strategic importance, and sound assessment of capabilities sometimes requires in-depth analysis. Accordingly, the paper takes a broad view of its scope, although not adequately addressing some issues (notably related to systems of systems [SoS], personnel, training, and operations planning) that are usually seen as subjects for other communities. Future work should address the substantial overlaps that increasingly exist across the M & S-using communities.