A weather balloon, also known as a sounding balloon, is a balloon that carries instruments to the stratosphere to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde. To obtain wind data, they can be tracked by radar, radio direction finding, or navigation systems. Balloons meant to stay at a constant altitude for long periods of time are known as transosondes. Weather balloons that do not carry an instrument pack are used to determine upper-level winds and the height of cloud layers. For such balloons, a theodolite or total station is used to track the balloon's azimuth and elevation, which are then converted to estimated wind speed and direction and/or cloud height, as applicable.

High-altitude balloons or stratostats are usually uncrewed balloons typically filled with helium or hydrogen and released into the stratosphere, generally attaining between 18 and 37 km above sea level. In 2013, a balloon named BS 13-08 reached a record altitude of 53.7 km.