The organisation of open primary elections by the political parties is a recent phenomenon in France. This system was adopted by the Parti Socialiste (PS) for the first time for the presidential election in 2012 with success. It was used as well for some local elections by both the PS and the Union pour un Mouvement Populaire (UMP) in 2014. It is likely be chosen by these two parties for the presidential election in 2017. This paper deals with new legal problems as there is an important issue today as regards the articulation between these new political tools, the political finance and the electoral law. The French law is very strict as regards to political campaign expenses. Besides, the problem to know if (and how) the costs of primary elections have to be included, or not, into the campaign accounts is not so clear. The interpretation of the judges and of the administrative authorities are different. A special difficulty is pending at the moment concerning the city of Marseille, because some campaign accounts could be rejected by the administrative authority (the CNCCFP). This paper deals with two crucial points. The first one is an explanation of the rules in political finance in France concerning open primary elections. The second one is a description of the potential effects of these rules on the political competition in France before the next presidential election. It is very likely there will be an important factor of limitation of open primary elections because of French law and this will influence the future political choices.