Parliament is responsible for approving new laws (legislation). The government introduces most plans for new laws, or changes to existing laws - but they can originate from an MP, Lord or even a member of the public or private group. Before they can become law, both the House of Commons and House of Lords must debate and vote on the proposals.
Bills normally introduce new laws. Bills that deal with more political or controversial issues usually begin in the Commons.
Defeating and delaying legislation
To become law the text of a Bill must be agreed by both Houses. Either House can vote down a Bill in which case it will normally not become law - but there are exceptions. The Commons can pass the same Bill in two successive years, in which case it can become law without the agreement of the Lords. Bills which are only about money (raising taxes or authorising government expenditure) are not opposed in the Lords and may only be delayed for a month.
The reigning monarch has to approve all new laws - called the Royal Assent - but this is a formality as in practice it is not withheld. Royal Assent was last withheld in 1708 when Queen Anne refused a Bill to settle the Militia in Scotland.
When a Bill is given Royal Assent it becomes an Act of Parliament. It is then the responsibility of the relevant government department to implement that law (eg, the Home Office will deal with new Acts relating to immigration).