This paper examines voting behaviour in the inaugural election to the National Assembly for Wales (NAW), held in May 1999. We address two questions: (i) why did the election produce a ‘quiet earthquake’ in Welsh electoral politics, with the nationalist Plaid Cymru denying the Labour party their expected majority in the Assembly?; and (ii) what broader lessons does this case-study offer for the study of elections in the UK under devolution? Drawing on data from the Welsh National Assembly Election Study, we find that while some features of second-order election theories, such as lower turnout and a lower vote share for the governing party were manifest, contrary to the predictions of such theories the surge in electoral support for Plaid was...