This paper presents an eigenvalue algorithm for accurately computing the Hausdorff. dimension of limit sets of Kleinian groups and Julia sets of rational maps. The algorithm is applied to Schottky groups, quadratic polynomials and Blaschke products, yielding both numerical and theoretical results. Dimension graphs are presented for (a) the family of Fuchsian groups generated by reflections in 3 symmetric geodesics; (b) the family of polynomials f(c)(z) = z(2) + c, c is an element of [ - 1, 1/2]; and (c) the family of rational maps f(t)(z) = z/t+ 1/z, t is an element of (0, 1]. We also calculate H.dim(Lambda) approximate to 1.305688 for the Apollonian gasket, and H.dim(J(f)) approximate to 1.3934 for Douady's rabbit, where f(z) = z(2) + c satisfies f(3)(0) = 0.