The ability of Members of Parliament (MPs) to know the policy preferences of their party voters is a precondition for substantive representation. This study investigates whether MPs' perceptions of their party voters' opinions are more accurate with policy statements on which they are competent—namely, those that are owned by their party and in which the MPs have specialised. It combines unique data from citizen surveys and face-to-face meetings with 367 MPs in Belgium, Canada, Germany and Switzerland. Both citizens and MPs evaluated the same statements, and MPs also estimated the support for each statement among their party voters. The comparison of party voters' preferences and MPs' estimations shows that MPs are more accurate on statements owned by their party, but not on issues they themselves specialise in through committee membership. Party issue ownership plays an important role in determining MPs' perceptual accuracy and, hence, democratic representation.