Amazon has been granted approval by the US federal aviation regulator to test its proposed delivery drone service.
The retailer revealed its plans to send packages to customers via drone in late 2013. It is developing drones that can fly at speeds of 50 miles per hour (80 kph), operate autonomously and sense and avoid objects.
Amazon was forced to ask permission from the US Federal Aviation Administration to test the service, which under existing rules was deemed illegal.
The company last year asked if it could test drones in outdoor areas near Seattle in the US, nearby one of its research and development labs.
The Federal Aviation Administration today said it had given approval to Amazon for its prototype drone design, which would allow the company to conduct outdoor test flights on private, rural land in Washington state.
The so-called "experimental airworthiness certificate" applies to a particular drone design. Amazon must get a new certification if it modifies the drone.
Conditions of the certificate stipulate that Amazon must supply monthly data to the FAA, and only conduct flights at 400 feet or below in "visual meteorological conditions".
In line with draft drone rules issued in February, those operating the drones must have a private pilots' license.
The FAA's long-awaited draft rules seek to address growing interest in commercial drone operators by setting guidelines for such services.
They will need to undergo public consultation for around a year before becoming formal.
Under the current proposed rules, pilots of the unmanned aircraft would need to obtain special pilot certificates, stay away from bystanders and fly only during the day.
Flying speed would be limited to 160 kph per hour and altitude to 152 metres above ground level.
Pilots would also need to remain in the line of sight of its radio-control drone, which could limit inspection of pipelines, crops, and electrical towers - one of the major uses envisioned by companies.