A method is presented for designing constant multivariable feedback controllers that make selected closed-loop eigenvaluesinvarianttounknownperturbations ofarbitrarymagnitude in system parameters. The sufficient conditions for eigenvalue invariance are expressed in terms of the structure of the closed-loop system matrices, and a numerical example is included to show how eigenvalue/eigenvector assignment techniques can be used to produce the desired eigenvector structure and thereby, eigenvalue invariance.