The legal analysis of the monetary union under construction in West Africa is important. It involves a comparative analysis of monetary unions in Europe and Africa in particular, taking as a paradigm the legal regime of their central banks and Mundell's theory of optimal monetary zones, in order to gain a better insight into the ECOWAS monetary union. Always following a forward-looking approach, the aim is to highlight potential obstacles, particularly political and legal ones. Solutions were then proposed to overcome these difficulties.