The Federal Diet of Switzerland (German: Tagsatzung, IPA: [ˈtaːkˌzatsʊŋ]; French: Diète fédérale; Italian: Dieta federale) was the legislative and executive council of the Old Swiss Confederacy and existed in various forms from the beginnings of Swiss independence until the formation of the Swiss federal state in 1848.
The Diet was a meeting of delegates from the individual cantons. It was the most wide-reaching political institution of the Old Swiss Confederacy, but its power was very limited, as the cantons were essentially sovereign.
While the composition and functions of the Federal Diet had changed and evolved since its founding in the 15th century, it was most notably reorganised during the Revolutionary and Napoleonic period. The understanding of the Federal Diet can be broken down into three main periods: before the French invasion in 1798, the period of the French invasion and the Act of Mediation, and from its restructuring by the Federal Treaty (Bundesvertrag) of 7 August 1815 to its dissolution after the Sonderbund War in 1848.