The Kipferl, ancestor of the croissant, has been documented in Austria going back at least as far as the 13th century, in various shapes. The Kipferl can be made plain or with nut or other fillings (some consider the rugelach a form of Kipferl).
The “birth” of the croissant itself – that is, its adaptation from the plainer form of Kipferl, before the invention of Viennoiserie – can be dated with some precision to at latest 1839 (some say 1838), when an Austrian artillery officer, August Zang, founded a Viennese bakery (“Boulangerie Viennoise”) at 92, rue de Richelieu in Paris. This bakery, which served Viennese specialities including the Kipferl and the Vienna loaf, quickly became popular and inspired French imitators (and the concept, if not the term, viennoiserie, a 20th-century term for supposedly Vienna-style pastries). The French version of the Kipferl was named for its crescent (croissant) shape and has become a identifiable shape across the world.