In the decades of the 20th century domestic and international tourism grew exponentially, often with a solid focus on cultural and natural heritage sites. The 1999 ICOMOS International Cultural Toursm Charter became a key basis for building cooperative links between ICOMOS and UNESCO World Heritage Office, UN World Tourism Organisation (UNWTO), International Union for the Conservation of Nature (IUCN) and many NGOs. A great many international and national workshops and conferences were held around the world as the dialogue between tourism and heritage sectors flourished.