The problem of solvency in insurance is at present under a good deal of discussion in various interested quarters, both national and international. It is principally a question of finding criteria for determining the size of the solvency margin which a private insurer must have in the form of free reserves to be considered solvent. A criterion must produce a margin which is both sufficient and suitable: it must be valid not only for a model portfolio but for any portfolio. Consequently, only insurers with the prescribed margin would be considered solvent and authorized to write insurance business. In recent years, particularly because of the directives promulgated by the Common Market authorities, it has largely been a question of the solvency of non-life insurers.