The federal bureaucracy plays a major role in the creation of laws. This is because they use the leeway given to them by Congress. When Congress writes laws, it typically leaves out many of the details. It does this in part because it lacks expertise in some areas and partly because it is politically easier to leave out details when writing laws. The details must then be filled in by the bureaucracy. For example, the Department of Education must write rules and make decisions about what exactly is required under the No Child Left Behind law. When it does so, it is making law even though Congress is officially the law-making body for the nation.