Britain has an uncodified constitution. This means that it is constituted from a variety of sources, including: Statute Law, Common Law, Conventions, Royal Prerogative, External Relations and Works of Authority. Of these sources, many are uncodified, meaning they are not written down. This contrasts to a codified constitution like that of the United States in which the vast majority of constitutional rules are contained within the US Constitution which was signed in Philadelphia in 1787.