Drones are coming to a patch of sky near you. Lots of them.

Consumers will buy between half a million and a million drones this holiday season, says Keith Kaplan, the co-founder and CEO of the Unmanned Aerial Vehicle Systems Association. That means that once all the presents under the tree are unwrapped, there will be more drones in existence than manned aircraft.

Over the weekend Kaplan's organization hosted the second-annual International Drone Expo in Los Angeles. The conference doubled in size this year, giving the world a glimpse into the future of an industry that market researcher IBISWorld estimates is now worth $3.3 billion. Companies displayed their newest products, from a drone that looks like Star Wars robot R2D2 to a new UAV from a company whose products were used to film parts of Pirates of the Caribbean.

Drones are "the most accessible business opportunity we've had in aviation in 60 years," Kaplan says, adding that some experts estimate that the value of the drone industry will reach $90 billion by 2025.

As the industry grows, the government is setting rules to encourage responsible drone operation. On Monday, the FAA announced that civilian drone operators must register drones weighing under 55 pounds with the agency by February 19. The FAA already had mandated that commercial drone pilots must obtain a sport pilot license, requiring $10,000 and 20 hours of experience flying a manned aircraft. However, the agency says it will soon create a commercial operator license with less onerous requirements. 

"Drones are aircraft. You wouldn't hand a 16 year old keys to a car without first making them practice driving for a year and learning how to operate it," Kaplan says.

The unmanned aerial vehicle boom has been driven by advancements in robotics and smartphone technology, such as mini sensors, gyroscopes, and automated software. Companies are entering the industry for a variety of reasons. Some are focusing on the hobbyist market, while others see opportunity in automating dangerous and tedious jobs like search-and-rescue missions and infrastructure inspection.

"If you think about what happened in the computer industry in the 1980s, you say 'The land of 1,000 garages,'" Kaplan says. "We are really at the land of 1,000 garages right now for the drone industry--entrepreneurs, engineers, scientists are all trying to figure out who in the world will be the next dominant player, the next drone billionaire."