National Route 40 or RN40, often called Ruta 40 even in English texts, is a route in western Argentina, stretching from Cabo Virgenes in Santa Cruz Province in the south to La Quiaca in Jujuy Province in the north, running parallel to the Andes mountains. The southern part of the route, a largely paved road through sparcely populated territory, has become a well-known adventure tourism journey.

Route 40 is the longest route in Argentina and one of the largest in the world (along with the U.S. Route 66 and the Stuart Highway in Australia -without counting the unofficial Panamerican Highway-) , more than 5,000 km (3,107 mi) long. At its traditional southern end near the city of Río Gallegos it starts at sea level, crosses 20 national parks, 18 major rivers, 27 passes on the Andes, and goes up to 5,000 m (16,404 ft) above sea level in Abra del Acay in Salta.

The road crosses the provinces of Santa Cruz, Chubut, Río Negro, Neuquen, Mendoza, San Juan, La Rioja, Catamarca, Tucumán, Salta and Jujuy.