SUMMARY: In treating this theme, the author divides his study in two sections: the ecume­nical dialogue and participation. The items dealt with in the first section are: the recognition of the ecclesiality and of the organised groups of non-Catholic Christians; legitimacy of their juridical order; admission of non-Catholics to full communion with the Catholic Church. The items treated in the second section are: participation in profane or civil affairs; participation in spiritual affairs; participation in sacred places; participation in sacred meetings; spiritual assistance to non-Catholic Christians; funeral service of a non-Catholic Christian; participa­tion in sacred functions; participation in the sacraments.