Electronic Journal of Differential Equations, Vol. 1999(1999), No. 36, pp. 1-13. Title: The effect of thin coatings on second harmonic generation Authors: Habib Ammari (Ecole Polytechnique, Palaiseau, France) Gang Bao (Michigan State Univ., East Lansing, MI, USA) Kamel Hamdache (Univ. de Paris, France) Abstract: The effect of thin coatings of nonlinear material on second harmonic generation is studied in this paper. Asymptotic expansions of the fields inside a thin nonlinear coating are performed. The convergence of these formal expansions is established. Our asymptotic analysis reveals the physical nature of this nonlinear problem. It also provides an effective method for overcoming the computational difficulties that arise in thin nonlinear coatings. Submitted May 30, 1999. Published September 20, 1999. Math Subject Classifications: 35C20, 78A45, 78A60. Key Words: Thin coatings; second harmonic generation; asymptotic analysis.