TITLE: A parameterization method for the computation of invariant tori and their whiskers in quasi periodic maps: rigorous results. AUTHORS: Alex Haro (1) and Rafael de la Llave (2) (1) Departament de Matematica Aplicada i Analisi, Universitat de Barcelona, Gran Via 585, 08007 Barcelona (Spain) E-mail: haro@mat.ub.es (2) Department of Mathematics, University of Texas at Austin, Austin, TX 78712 (USA). E-mails: llave@math.utexas.edu ABSTRACT: We prove rigorous results on existence and persistence of invariant tori and their invariant manifolds for quasiperiodically perturbed systems. The proofs are based on the parametrization method of X. Cabre, E. Fontich, R. de la Llave, Ind. Math. Jour. 52, 2. The invariant manifolds results proved here include as particular cases of the usual (strong) stable and (strong) unstable manifolds, but also include other non-resonant manifolds. The method lends itself to numerical implementations whose analysis and implementation is studied in several companion papers by the same authors.