This text grew up from lecturcs givcn at he t University of Rennes I during the academic year 1988-1989. The main topics covered arc second microlocalization along a agrangian l manifold, defined by Sjostrand in [Sj], and its application to the study of conormal sin- gularities for solutions of semilinear hyperbolic partial differential equations, developed by Lebeau [L4]. To give a quite self-contained treatment of these questions, we induded some de- velopments about FBI transformations and subanalytic geometry. The text is made oi four chapters. In he t first one, we define the Fourier-Bros-Ingolnitzer transionnation and study its main properties. The second chapter deals with second microlocalization along a lagrangian submanifold, and with upper bounds for the wave front set of traces one may obtain using it. The third chapter is devoted to formulas giving geometric upper bounds for the analytic wave front set and for the ser,ond mic:rosllpport of boundary values of ramified functions.Lastly, the fourth chapter applies the preceding methods to the derivation of theorems about the location of microlocal singularities of solutions of scmilinear wave equations with conormw data, in general geometrical situation. Every chapter begins with a short abstract of its contents, where are collected the bibliograph- ical references. Let me now thank all those who made this writing possible. First of all, Gilles Lebeau, from whom I learnt mcrol i ocal analysis, especially through lectures he gave with Yves Laurent at Ecole Normale Superieure in 1982-1983.
