Abstract : In this Thesis, we report on the study of Bose-Einstein condensates in anisotropic traps. First, the behavior of the thermal cloud is investigated for temperatures close to the condensation threshold. A shift in the critical temperature and a reduction of the condensed fraction due to interactions are observed, in good agreement with a Hartree-Fock theory of the mixed cloud. A second study focuses on the extraction and propagation of atom lasers created through radio-frequency output coupling. Measurements of the transverse divergence identify as the primary contributor the mean field exerted by the condensate on the outcoupled atoms. The third part is devoted to the study of phase fluctuations in very elongated (quasi-)condensates through Bragg spectroscopy of the momentum distribution. We observe a Lorentzian lineshape of the momentum distribution, characteristic of strongly phase-fluctuating samples. Measurements of the momentum width, along with the observation of suppressed density fluctuations when compared to a thermal-like distribution, confirm the validity of the Bogoliubov approach to describe low-dimensional quasi-condensates.