MEMS design tools are increasingly important as micro systems find wider applications. Though established structured design methodologies are in place for VLSI design, these tools cannot be applied to MEMS design without adaptation.Several needs must be met to enable MEMS design: (1) non-linear, dynamic and multi-energy domain design and simulation;(2) expression of complex and curvilinear geometries; (3) arbitrary orientation and placement of MEMS components; and (4) comprehensive, three-dimensional visualization and analyses.We describe a structured design methodology for MEMS CAD that addresses the non-separable, helical nature of MEMS device and system design, including both top-down and bottom-up strategies. The iterative design process integrates custom layout, synthesis, verification and optimization with model building and library construction. Our integrated MEMS CAD suite includes libraries of MEMS device components and their models and tools for: (a) physical design, (b) mixed-domain FEIBE analysis, (c) placement and routing synthesis, (d) macromodel construction, (e) schematic design entry and system level behavioral simulation , and (I) layout extraction and design rule checking verification. The tools are demonstrated on designs of micro-resonators. Simulated and fabricated devices are compared. MEMS Pro is used to design devices and systems and predict their performance.