The Federal Charter or Letter of Alliance (German: Bundesbrief) is one of the earliest constitutional documents of Switzerland. A treaty of alliance from 1291 between the cantons of Uri, Schwyz and Unterwalden, the Charter is one of a series of alliances from which the Old Swiss Confederacy emerged. In the 19th and 20th century, after the establishment of the Swiss federal state, the Charter became the central founding document of Switzerland in the popular imagination.

The Charter documents the Eternal Alliance of the League of the Three Forest Cantons (German: Ewiger Bund der Drei Waldsttten), the union of three cantons in what is now central Switzerland. It is dated to early August 1291, which in the 20th century inspired the date of Swiss National Day, 1 August. Done in Latin, the Charter makes reference to a previous (lost or unwritten) pact. It is now exhibited at the Museum of the Swiss Charters of Confederation in Schwyz.

The Old Swiss Confederacy or Swiss Confederacy (Modern German: Alte Eidgenossenschaft; historically Eidgenossenschaft, after the Reformation also Corps des Suisses, Confoederatio helvetica "Confederation of the Swiss") was a loose confederation of independent small states (cantons, German Orte or Stände) initially within the Holy Roman Empire. It is the precursor of the modern state of Switzerland.

It formed during the 14th century, from a nucleus in what is now Central Switzerland, expanding to include the cities of Zürich and Berne by the middle of the century. This formed a rare union of rural and urban communes, all of which enjoyed imperial immediacy in the Holy Roman Empire.

This confederation of eight cantons (Acht Orte) was politically and militarily successful for more than a century, culminating in the Burgundy Wars of the 1470s which established it as a power in the complicated political landscape dominated by France and the Habsburgs. Its success resulted in the addition of more confederates, increasing the number of cantons to thirteen (Dreizehn Orte) by 1513. The confederacy pledged neutrality in 1647 (under the threat of the Thirty Years' War), although many Swiss served privately as mercenaries in the Italian Wars and during the Early Modern period.

After the Swabian War of 1499 the confederacy was a de facto independent state throughout the early modern period, although still nominally part of the Holy Roman Empire until 1648 when the Treaty of Westphalia ended the Thirty Years' War. The Swiss Reformation divided the confederates into Reformed and Catholic parties, resulting in internal conflict from the 16th to the 18th centuries; as a result, the federal diet (Tagsatzung) was often paralysed by hostility between the factions. The Swiss Confederacy fell to invasion by the French Revolutionary Army in 1798, after which it became the short-lived Helvetic Republic.