In the UK weather balloon flight permission is granted by the CAA, to get permission you need to fill in this Application form and send it to them at least 28 days in advance (even earlier if possible) with a photocopy of an OS Map with the launch site marked. Due to the changable UK weather it is worth applying for a 'window' of possible launch times - such as a couple of weekends.

The actual situation is not that you are applying for permission but instead being granted exemption from the Air Navigation Order 2005 surround the launching of balloons. The regulations require the use of a standard meterological balloon and for the payload to descend by parachute.

In the UK, OFCOM regulations stipulate that amateur radio cannot be used in airborne applications. As such, license free modules must be used - though not all license exempt modules are permitted to be used in air to ground communications. See license exempt for more information.

Regulations may vary in other countries - ie American and Australian legislation appears to allow the use of amateur radio transmitters in airborne applications. Don't take this as gospel - check with your local regulator.