Despite the abundance of studies of Polish migration to the UK immediately before and in the aftermath of accession to the EU in 2004, one fundamental question has never been clearly answered: why did so many Poles move to the UK? We have sought to provide general explanations, rather than inquiring into the range of observed diversity. We begin by putting together statistical and other data from both ends of the flow in order to assess the scale of movement to and from the UK and to determine the reasons for what may well have been the largest voluntary migration between two countries. We used data from both countries and especially the recently published statistics from the 2011 UK census to present a detailed picture of the characteristics of those involved. Polish statistics suggest a more ‘elite’ flow to the UK than to other countries. The UK census pictures a maturing settled population, still tending to occupy relatively lower skilled jobs but showing evidence of upward social mobility. The movements are particularly a response to demographic and economic factors in Poland and to a widespread but to some extent hidden shortage of labour in some sectors in the UK. These factors combine with a set of political circumstances in both countries to produce an explanatory framework that may be summarised as ‘right people, right place, and right circumstances.’