Abstract : The characteristic Cauchy problem for linear wave equations consists of imposing initial values for the solution on a characteristic hypersurface instead of initial values for the function and its normal derivative on a spacelike Cauchy hypersurface. After a general introduction to the relevant notions we show that this problem is well posed on globally hyperbolic Lorentzian manifolds under suitable assumptions. This is joint work with Roger Tagne Wafo and it generalizes classical results by Hörmander.