We present a review of our research activities concerning the proton exchange technique on lithium niobate and lithium tantalate for integrated lasers and nonlinear frequency converters. In the first part we present the material characterizations that allowed us to establish the phase diagram of the proton exchanged layers on both crystals. In the second part we show how the knowledge of these phase diagrams allows us to understand and handle the problem of the reduction of the excited-state lifetime of the rare-earth ions in Nd- and Er-doped crystals. In the third part, we describe the influence of the different proton exchange processes on the nonlinearity and the domain structure of periodically poled crystals, which leads us to recommend the use of waveguides fabricated using low-acidity melts, which preserves both the nonlinear coefficient and the domain structure. © 1998 Society of Photo-Optical Instrumentation Engineers.