Electrostatic charging of balloons and gondolas is frequently observed, especially during ascents in the atmosphere. Charge buildup modifies the potential distribution of the environment and perturbs the measurements of quasi-static fields with electric antennas and of atmospheric conductivity with Langmuir probes and relaxation probes. The magnitude of the surface charging is a function of altitude, vertical velocity, body size, and geometry; the polarity of the potential may differ during ascent and descent. An explanation is proposed for the mechanisms responsible for this complex phenomenon, where aerosol, turbulence, loss of negative ions, and downward fair weather electric field play critical roles. This model is supported by experimental results collected during balloon flights dedicated to the investigation of atmospheric electricity. The possible consequences for the measurements to be performed during the descent of the Huygens Probe in the atmosphere of Titan are briefly discussed. ¿ 1998 American Geophysical Union