A constitution is the fundamental and supreme law of a society. Governments and based upon rules or guidelines that determine how they are organized and what powers they have. These rules matter because they define the relationship among the people in a society ;they determine what each person is entitled to expect from the other-and from the government. And no rules matter more than those embodied in a nation's constitution. The United states has a written, all in one document (unlike the constitution of Great Britain, which is a partly written, partly unwritten body of various declarations, statutes, practices, and precedents).
But just because a constitution is written does not necessarily mean that it will be followed and enforced. Some countries have constitution that have not proven to be reliable guarantees against illegal takeovers and rule of force. If a nation's constitution is to be effective in restraining government and protecting citizens' rights, it must enjoy general respect and support from the citizens of the country. Ours does. It is the oldest living written constitution in the world, 200 years old in 1987.