The Long Parliament was an English Parliament which lasted from 1640 until 1660. It followed the fiasco of the Short Parliament, which had convened for only three weeks during the spring of 1640 after an 11-year parliamentary absence. In September 1640, King Charles I issued writs summoning a parliament to convene on 3 November 1640. He intended it to pass financial bills, a step made necessary by the costs of the Bishops' Wars in Scotland. The Long Parliament received its name from the fact that, by Act of Parliament, it stipulated it could be dissolved only with agreement of the members; and those members did not agree to its dissolution until 16 March 1660, after the English Civil War and near the close of the Interregnum.The parliament sat from 1640 until 1648, when it was purged by the New Model Army. After this point, the remaining members of the House of Commons became known as the Rump Parliament; Oliver Cromwell disbanded the Rump in April 1653, replacing it with a succession of nominated and elected parliaments.

In the chaos following the death of Cromwell in September 1658, the Rump was reinstalled in May 1659, and in February 1660 General George Monck allowed the members barred in 1648 to retake their seats, so that they could pass the necessary legislation to allow the Restoration and dissolve the Long Parliament. This cleared the way for a new parliament to be elected, which was known as the Convention Parliament. Some key members of the Long Parliament, such as Sir Henry Vane the Younger and General Edmond Ludlow, were barred from the final acts of the Long Parliament. They claimed the parliament was not legally dissolved, its final votes a procedural irregularity (words used contemporaneously were "device" and "conspiracy") by General George Monck to ensure the restoration of King Charles II of England. On the restoration the general was awarded with a dukedom.

The Long Parliament later became a key moment in Whig histories of the seventeenth century. American Whig historian Charles Wentworth Upham believed the Long Parliament comprised "a set of the greatest geniuses for government that the world ever saw embarked together in one common cause" and whose actions produced an effect, which, at the time, made their country the wonder and admiration of the world, and is still felt and exhibited far beyond the borders of that country, in the progress of reform, and the advancement of popular liberty. He believed its republican principles made it a precursor to the American Revolutionary War.

Acts of parliament, sometimes referred to as primary legislation, are texts of law passed by the legislative body of a jurisdiction (often a parliament or council). In most countries with a parliamentary system of government, acts of parliament begin as a bill, which the legislature votes on. Depending on the structure of government, this text may then be subject to assent or approval from the executive branch.