Every EU Member State maintains a national representation to the EU in Brussels in addition to their normal embassies. This is known as the "Permanent Representation" of the Member State in question, or in Eurospeak: "The Rep".
The Council of Permanent Representatives, COREPER, prepares much of the business dealt with at the meetings in the EU Council of Minister, and it decides on 15% of the laws itself. 70% are decided upon by 297 Council working groups, which are often staffed by employees from the national representations. Only 15% are agreed upon by the Member States' ministers in the Council of Ministers itself.