Weather balloon & Radiosonde is a group of instruments for simultaneous measurement and radio transmission of meteorological data, including temperature, pressure, and humidity of the atmosphere.

The instrument package is usually carried into the atmosphere by a balloon. Balloon-borne radiosondes can reach altitudes as great as 90,000 ft (27,400 m) above the earth's surface. A radiosonde may also be carried by a rocket, in which case it is known as a rocketsonde, or dropped by parachute (usually from an aircraft), in which case it is known as a dropsonde. Instruments included in a radiosonde are typically transducers for humidity, temperature, and pressure measurements; controls to improve return signals and determine which measurements are to be transmitted to data stations; and a radio transmitter. Radar also has been used to measure and transmit meteorological data from a radiosonde. These radiosonde observations are made as often as two times daily at some meteorological stations around the globe.