Sustainable tourism is a concept that has been gaining traction in recent years, and which the United Nations is invested in promoting. They’ve even declared 2017 as the International Year of Sustainable Tourism for Development.

Tourism has grown rapidly in the last two decades. In 2000, 674 million people traveled internationally, and by 2015 that number had risen to 1.2 billion. That’s about one in seven people, globally, who are traveling outside their countries each year. The number is expected to hit 1.8 billion by 2020.

With so many people traveling, it’s important that we find ways to make sure that tourism has a positive impact on the world.

Historically, tourism has had a lot of negative impacts, with travelers treating their destinations as “exotic” or “savage” places, where they couldn’t be bothered to care about the effects they had on local culture or ecology. But we’ve come a long way since the British Empire—and even since the 1970s, when caring about the ecological impact of travel or having an interest in local culture was considered hippy nonsense.

Sustainable tourism refers to trying to make the best of travel by utilizing environmentally friendly practices, protecting natural space and cultural heritage, and supporting the communities that host hotels and resorts by employing locals and giving back to the people who live there.

Throughout the travel industry, a number of companies are trying to do exactly that by thinking more critically about their practices–even cruise ships, among the most notorious of polluters, are getting into the game by installing scrubbers in their ships’ exhaust systems and buying sustainably harvested seafood–but there are still many that aren’t concerned with helping the environment or local communities. This is partly because not enough customers are worried about the sustainability or impact of their tourism, something that needs to change.

Companies tend to respond to customer demand, so if more people start expressing concerns about how ecologically sound or culturally respectful a travel package is, more companies will do more to promote sustainable tourism.