Regulation, governance and organisational issues are sensitive aspects in the market of public utilities especially when these markets require and aim at initiating homogenisation processes.The paper aims at understanding how European countries responded to supranational legislation, in terms of governance, management and organisational aspects, on the establishment of Railway Regulatory Bodies and if the steps taken by the European Union were sufficient to fulfil the aim of creating an integrated railway area.We use a neo-institutional lens to interpret documentary sources, such as regulatory sources (Regulations, circulars and directives of the EU) and the responses given to a semi-structured questionnaire submitted to the 28 European Railway Regulatory Authorities.The paper shows that this regulatory field faced differentiated isomorphism and that there is a growing trend towards an organisational model we characterised as ‘Generalist Agency’.We contribute to the literature on the regulation of public utilities, showing that differentiated isomorphism may occur when coercive isomorphism by supranational legislation is mitigated by national differences, and provide policy implications on governance and regulation of the transport industry.