Aviation regulators have given Amazon the official go-ahead to begin testing its Prime Air drones in the United States — a decision that, together with a new federal approval process, could also pave the way for other companies interested in drone delivery.

The Federal Aviation Administration told Amazon Wednesday that it will be free to conduct research and development on drone technology, with certain restrictions. Amazon's drones can't fly higher than 400 feet or faster than 100 miles per hour. They'll also have to remain within the drone operator's direct line of sight, fly only during the day and operate over private property.

The two-year exemption lets Amazon push ahead with its plans to ship small packages by drone. The company hopes cutting down the wait time between order and delivery will encourage consumers to buy more online.

"We’re pleased the FAA has granted our petition for this stage of R&D experimentation, and we look forward to working with the agency for permission to deliver Prime Air service to customers in the United States safely and soon," said Paul Misener, Amazon's vice president for global public policy.

Although Amazon had already gotten FAA permission to test an earlier drone prototype, according to Reuters, that approval came far too late to be useful — by then Amazon had already moved on to a newer prototype. The FAA's latest exemption lasts for two years.

Amazon isn't the only company that's dreamed of delivering goods with unmanned aerial vehicles. From beer to pizza to tacos, drone delivery could be applied to many industries. That's why Amazon's exemption is so important, and why a new program from the FAA to streamline requests for exemptions could open the door to many drone delivery businesses.

The FAA announced this week that it's beginning to offer "summary grants" of approval for drone use — a faster method of processing applications that bypasses the typical evidence-gathering and analysis procedures. The agency said the fast-track method will be used in situations where a pending application is judged to be similar to a previous application that's already been granted.

Now that Amazon has gotten approval to do R&D for drone delivery, others wishing to do the same might get expedited treatment under the summary grant process. But, said FAA spokesperson Les Dorr, each application will still be evaluated individually.

"We are trying to be as flexible as possible with the summary grants, but it really depends on the applicant’s proposed operation," said Dorr.