In 1659, Luis de Haro met with Cardinal Jules Mazarin in the Pyrenees to conclude a peace treaty and marriage agreement that would end over twenty years of war between Spain and France. The hitherto unpublished letters which Haro sent to Philip IV from the peace conference are fascinating to read and offer an account of the negotiations that often diverges radically from what Mazarin reports in his letters to the French court. This edition offers a mix of the original letters and summaries of the letters, as well as numerous explanatory notes and an introduction that sets the peace conference firmly within its historical context. This volume in the Exeter Hispanic Texts series provides the letters in the original Spanish; the Introduction, notes and summaries are in English. It will be of interest to a scholarly readership, especially those concerned with late seventeenth-century Spanish and French history.