Do political parties respond to shifts in the preferences of their supporters, which we label the partisan constituency model, or to shifts in the mean voter position (the general electorate model)? Cross-national analyses — based on observations from Eurobarometer surveys and parties’ policy programmes in 15 countries from 1973 to 2002 — suggest that the general electorate model characterizes the policy shifts of mainstream parties. Alternatively, when we analyse the policy shifts of Communist, Green and extreme Nationalist parties (i.e. ‘niche’ parties), we find that these parties respond to shifts in the mean position of their supporters. The findings have implications for spatial theories and political representation.