This research work is devoted to the analysis of financing decisions of French Very Small Businesses (VSB).The first chapter of this thesis describes the object of the study, namely the VSB. The second chapter revisits the main theories of capital structure in the light of the specificities of VSBs, and motivates the use of the theoretical framework proposed by the Pecking Order Theory. The third chapter tests the Pecking Order Theory on a large sample of French VSBs. The fourth chapter suggests adapting this theory to the evidence of financing choicesand financial constraints of VSBs, particularly by incorporating an infra-debt hierarchy. This chapter also provides an empirical test of the trade off between financial debts and partners' current accounts. The main contribution of this work is certainly the generalization of the Pecking Order Theory to the French VSB universe. These firms prefer internal financing to external financing, and debt to issuing shares. However, firms with excess of financing do not try to reduce debt quickly, which can be translated by the anticipation of future financing deficits, which become even more severe as these businesses are subject to credit rationing.Nevertheless, the Pecking Order Theory still does not provide any explanation for the preference of the VSBs’ managers for financial debt, compared to partners' current accounts. The fact that VSBs are generally owned and managed by the same person makes it possible to analyze their financial behavior under the diversification theory. Share holder-managers prefer diversifying their personal wealth rather than minimizing costs of information asymmetry