The Treaty of Noyon (13 August 1516) ended the fighting between Spain and France after Francis I's first invasion of Italy. The most important terms of the treaty were that Charles I of Spain (the future Charles V) acknowledged French control of Milan, while Francis I agreed to pass his claim to Naples to Charles through a marriage alliance.
When Francis had invaded Italy in 1515 Spain had been ruled by Ferdinand the Catholic, but he died in January 1516 and was succeeded by his young grandson Charles. He ruled as Charles I of Spain, but is better known by his later title of the Emperor Charles V. Francis had already won control of Milan through his victory at Marignano (13-14 September 1515), and Charles's advisors in the Netherlands were opposed to any war for purely Italian aims.
The Treaty of Noyons saw Charles acknowledge Francis's position in Milan. Francis didn't actually repudiate his claim to Naples, but he did agree to pass it to Charles through a marriage alliance. This had also been the solution used at the Treaty of Blois in 1505, when the French claim to Naples had been made part of the dowry of Germaine de Foix, the second wife of Ferdinand of Aragon. When the marriage ended without producing an heir that claim reverted to France.
Charles was to marry Francis's infant daughter Princess Louise. If the princess died before the marriage could take place then Charles was to marry either any future daughters of Francis, or Renée, the daughter of Louis XII. Whichever bride Charles ended up marrying would bring with her the French claim to Naples. In return Charles would pay a pension to Francis until the marriage had produced a son. If there was no marriage then the French would keep their claim to Naples.
Charles also promised to satisfy the dispossessed King John III of Navarre, who had lost the Spanish part of his kingdom to a Spanish invasion in 1512.
The Treaty of Noyons left the Emperor Maximilian isolated in Italy. The Swiss had made peace after their defeat at Marignano, the Pope soon afterwards and Spain and the Netherlands were out after this treaty. Maximilian attempted one last invasion of Lombardy, but after this failed made peace himself in the Treaty of Brussels (4 December 1516).
The Treaty of Noyons stood for peace between France and the Netherlands, and wasn't popular in Spain where the possible surrender of Spanish Navarre was seen as a sign that Charles wasn't supporting their rights.
The key clause was never implemented. Princess Louise died in 1517. By then there was a second sister, Charlotte, born in 1516. Charles was engaged to her, but sadly she also died young, in 1524. By then Charles and Francis were at war (First Hapsburg-Valois War), and Charles had already moved on, becoming engaged to the young Mary Tudor in 1522. This marriage also failed to take place and instead he married his first cousin Isabella of Portugal in 1526.
By the time Charles travelled to England in 1520 the treaty was losing its relevance. In the previous year he had been elected as Holy Roman Emperor, increasing his powers, but also antagonising Francis, who had also wanted the title. Francis has already demanded that the terms of the treaty be implemented quickly, but this was not to be.