A technique of constrained eigenstructure assignment (CEA) is presented. The technique can update small order finite element models by using experimental modal analysis data or assign analytical eigenstructure to dynamic models for purposes of simulation and design. The CEA technique forms symmetric damping and stiffness correction matrices that mirror the form of the existing model. Non-zero entries in the upper triangular parts of the correction matrices become design variables and are optimized to assign the desired eigenstructure. A common problem in updating methods is the loss of physical connectivity and matrix symmetry. The method proposed here retains matrix symmetry and banding, and the signs of the diagonal and off-diagonal elements, and can bound the magnitude of any entries of the coefficient matrices. Furthermore, the method can maintain the identities between repetitive entries in the matrices that occur due to symmetries in the geometry of the model. This is important when identical sections of a model should have identical stiffness and damping in the updated model. Also, this repetitiveness can substantially reduce the computational time of the solution. The CEA technique also incorporates an optional eigenvector iteration feature that minimizes shifting of unassigned eigenvalues. This is important for design purposes and when assigning only a few measured eigenvalues to the analytical model. A computer algorithm completely contained within the framework of the Matlab software system has been developed to implement the method. Simple example problems are presented to exhibit the utility of the technique. Note that the method presented here is most applicable to small or reduced order dynamic models, as large dimensions render the computations very slow.