Abstract : The subject of this mainly methodological thesis is the use of quantum trajectories, defined by de Broglie and Bohm, in studing molecular dynamical processes. Two kind of studies are presented. On the first hand, we use the quantum trajectories to solve the hydrodynamical form of the Schrödinger equation. A numerical method which combine the use of a fixed grid and moving grids was developed and applied to the photodissociation of the H2 molecule. This method is numerically efficient, especially for process like direct dissociation. On the second hand, we use quantum trajectories to establish a new hybrid quantum / classical propagation scheme. Methods of this kind are useful to treat the dynamics of systems too large to be treated by quantum mechanics, but where however at least some degrees of freedom require a quantum treatment. In our method, the positions associated with the quantum trajectories are used in the equation for the classical degrees of freedom to calculate their reaction to the quantum part. The results obtained on three systems, simple enough to have access to the exact results, are compared to those obtained by other hybrid schemes already widely used.