Let R ∈ C n×n be a nontrivial involution; i.e., R = R −1 / = ±I . We say that A ∈ C n×n is R-symmetric (R-skew symmetric) if RAR = A (RAR = −A). Let S be one of the following subsets of C n×n : (i) R-symmetric matrices; (ii) Hermitian R-symmetric matrices; (iii) Rskew symmetric matrices; (iv) Hermitian R-skew symmetric matrices. Let Z ∈ C n×m with rank(Z) = m and = diag(λ 1 , . . . , λ m ).The inverse eigenproblem consists of finding (Z, ) such that the set S(Z, ) = {A ∈ S|AZ = Z } is nonempty, and to find the general form of A ∈ S(Z, ). In all cases we use the special spectral properties of S to essentially characterize the set of admissible pairs (Z, ), and the special structure of the members of S to obtain the general solution of the inverse eigenproblem.Given an arbitrary B ∈ S, the approximation problem consists of finding the unique matrix A B ∈ S( , Z) that best approximates B in the Frobenius norm.It is not necessary to assume that R = R * in connection with the inverse eigenproblem for R-symmetric or R-skew symmetric matrices. However, we impose this additional assumption in connection with the inverse eigenproblem for Hermitian R-symmetric or R-skew symmetric matrices, and in connection with the approximation problem for (i)-(iv).