Highly Flexible Structures (HFSs) are designed to undergo large displacements without plastic deformation under normal operation conditions. HFSs have been used in many mechanical systems, civil structures, aerospace vehicles, and large space structures to satisfy space limitations, provide special mechanisms, and/or reduce structural weight. However, today's HFSs are very often built by trial and error and full-size testing. The objectives of this project are: (1) to derive and add new geometrically exact structural elements into the nonlinear finite-element code GESA for performing simulation-based design, analysis, and optimization of highly flexible isotropic and composite structures; (2) to derive efficient numerical methods for nonlinear static and dynamic analyses of HFSs; (3) to develop a MATLAB toolbox having graphical input and output for iteration of design, analysis, and dynamic animation; and (4) to perform experiments and establish an adequate database of post-buckling characteristics of HFSs and to derive guidelines for designing HFSs. This work is important for advancing the knowledge of nonlinear statics and dynamics of HFSs and for designing HFSs. This work will solve critical modeling issues, develop accurate modeling techniques for the design and analysis of HFSs, and provide an efficient tool for performing virtual experiments and rapid prototyping of HFSs.