The United Kingdom is a constitutional (or parliamentary) monarchy, without a written constitution. The British constitution is based on Acts of Parliament (also called «laws» or «statutes») and «conventions», which are commonly accepted assumptions about the way things should be done. The country has a monarch (a king or a queen) as its Head of State. The monarch has very little power and can only reign with the support of parliament. Parliament consists of two chambers known as the House of Lords and the House of Commons. Parliament and the monarch have different roles in the government of the country, and they only meet together on symbolic occasions such as the coronation of a new monarch or the opening of Parliament. In reality, the House of Commons is the only one of the three which has true power. It is here that new bills are introduced and debated. If the majority of the members are in favour of a bill it goes to the House of Lords to be debated and finally to the monarch to be signed. Only then does it become law. Although a bill must be supported by all three bodies, the House of Lords only has limited powers, and the monarch has not refused to sign one since the modern political system began over 200 years ago.