Tourism is currently the world's largest industry, generating over $3 trillion in annual revenues. It has evolved from early forms of travel for basic needs to modern travel for pleasure and exploration as technology advanced modes of transportation. The key components of tourism include transportation, accommodation, food and beverage, retail, and entertainment. There are various forms of tourism such as inbound, outbound, and domestic tourism as well as different categories including seaside, mountain, eco, wildlife, sports, heritage/cultural, health, medical, visiting friends/relatives, religious, and business tourism.