This paper analyses the information sources members of the Dutch Lower House base their questions on with regard to EU affairs in the period 1995-2013. Knowledge of the type of information sources to base questions on is vital for determining what the conditions are under which members of national parliaments can scrutinize the decisions taken by the national government at the EU level. The involvement of national parliaments in EU affairs is according to many scholars a necessary condition for closing the democratic deficit of the European Union, especially when the turnout in elections for the European Parliament remains low and for national parliaments remains stable and relatively high. An original dataset is constructed including all sets of written parliamentary questions on EU affairs asked by Dutch MPs in the period 1995-2013, categorized by different types of information sources on which the question is based. These different categories of information sources are regressed with a variable measuring the Treaty changes impacting on the intensity of contact between MPs of different national parliaments and several variables measuring the characteristics of Dutch MPs and their parties. The findings indicate that Dutch MPs base their written questions primarily on coverage on EU affairs by national newspapers. Moreover, MPs are more likely to use sources rooted in a national context for asking questions when they are a member of a party with a negative attitude towards European integration. These findings imply that parliamentary control via written questions over the decisions of the national executive at the EU level can be strengthened by increasing national media coverage on EU affairs, allowing the EU public sphere to develop further in the future.