In 2010, France and Germany introduced a common optional matrimonial property regime of participation in acquisitions in both countries. One of its goals was to establish European harmonization, up until then a rare occurrence in the broad field of family law. The harmonization journey was continued by Belgium in 2018, when the Franco-German agreement was taken over in the Belgian Civil Code. This article evaluates the Franco-German regime from both an internal and an external point of view in order to determine the success of this operation. In the internal analysis, the regime will be presented as a modern and balanced compromise between the French and German domestic participation in acquisition regimes. In the external analysis, the regime will be qualified as a legal transplant in Belgium that at this moment in time does not survive the operation. Despite this seemingly negative evaluation, the regime may still increase its success rate, provided all actors involved take the required measures. In any case, the regime should be welcomed as harmonization initiative, considering that new projects may learn from its successes as well as from its stumbling blocks.