New York City not too long ago had a landfill you could see from space. Now it has a plan to get to “zero waste” in the next 15 years–a task that might seem impossible to anyone who has wandered the city’s litter-strewn streets on a weekend and tried to find a public trash can that’s not overflowing.

So how does the nation’s largest city go about getting rid of its garbage? And what is zero waste anyway? Since the term became a buzzword two decades ago, it’s been adopted as a goal by many cities around the world. In practice, however, “zero” is a goal that’s out of reach for even the most well-meaning cities. They can go far–even to 90% reduction of landfill waste–but the last bit requires a higher-level of change than cities can usually achieve, such as getting more industries to design their products for zero waste in the first place.

But there are a few cities around the world that have become leaders in the zero-waste movement. While New York City has gotten a start–with a pilot composting program and a long-needed ban on styrofoam containers–it still has a long way to go.

San Francisco became the largest U.S. city to commit to zero waste in 2002, promising to divert 100% of its waste from landfills by 2020. Likely, it will be the first to come close to this goal. Doing this, according to the Guardian, has taken “great political determination,” including passing unpopular legislation (such as banning plastic bags and making composting mandatory) and working with restaurants, hotels, landlords, and the construction industry to get them to participate. It’s helped that the city had a good partner in the employee-owned, local waste management company Recology, which, for example, offers 20% discounts to residents who skip waste collection days twice a month.

Today, at more than 80% landfill diversion, San Francisco is well on its way to zero waste, but the last bit may be the hardest. The city says it can get to 90% landfill diversion by continuing its current activities. The last 10%, however, will require state or national laws that require or incentivize more product manufacturers to get on board with the program.

Sweden (and every city in it) has a slightly different approach to zero waste. It fuels itself off of trash, burning about 2 million tons of trash a year in waste-to-energy plants, replacing a not-insignificant amount of the nation’s fossil fuel use, and drastically reducing landfill waste. This, however, has a caused a problem: Sweden has also become so efficient at recycling and reducing waste that it doesn’t have enough trash to burn to power its facilities. It imports about 800,000 tons of trash annually from neighboring countries to feed its incineration plants.

As the Huffington Post notes, Sweden’s success was rooted in a cultural shift around attitudes towards trash that began in the 1970s and took decades to bear fruit.