During the accession process to the European Union, the European Commission introduced a new form of institution-building assistance to the candidate countries called twinning. Under these schemes public servants of some Member State were seconded to the parallel governmental office of the future Member State in order to facilitate, with hands-on public sector experience, the massive policy transfer embodied in the acquis communautaire. The paper discusses the overall positive experience of twinning projects based on past evaluations and interviews with Hungarian partner institutions and suggests that the ability of beneficiary institutions to absorb external assistance, the institutional inertia and the commitment of the organisation sending the long-term experts are the key limiting factors. These barriers are of relevance if twinning is to be used in other contexts such as cooperating on the implementation of climate policies. Twinning can support but not replace political willingness and perseverance.