The rationale for Ka-band propagation studies is discussed, and the relevant measurement program carried out in Germany by the Research Centre of the Deutsche Bundespost Telekom is reviewed. Current problems are briefly presented. Radiometer measurements from a 30 GHz site diversity experiment are discussed. The results indicate that availabilities of 99.9% can be achieved with diversity spacings of about 15 km. If, however, much lower values of around 97-99% are acceptable, margins of 3 dB are sufficient in single-site operation with gaseous and cloud absorption being of similar statistical importance as rain. Measurements carried out with the OLYMPUS satellite at 12.5, 20, and 30 GHz are also discussed. A comparison with the predictions based on the current CCIR procedures shows that rain attenuation is overestimated for time percentages above 0.01%, whereas depolarization is underestimated significantly. Instantaneous frequency scaling of attenuation and scintillations is discussed, and an improved scaling procedure for the latter is presented.>