National audienceDifferent hypotheses about the causes which have lead management to the use of smoothing practices have been proposed. Its basis rests on the general improvement of the shareholder's welfare as the dampening of the variability of the earning lessens the uncertainty of the excepted cash-flows. But the efficiency market hypothesis assumes that investors are note fooled by accounting manipulations. In this setting, accounting income smoothing is not justified. However, signalling theory and agency theory give some explanations for the income smoothing that agree with the investors' rationality.Différentes hypothèses sur les causes qui conduisent les dirigeants à des pratiques de lissage des résultats ont été proposées. Général...