The paper gives a brief description of the principles and the uncertainty of the acousticcalibration methods that today are applied by National Metrology Institutes andcalibration service centers. Even if some of the calibration principles have been appliedover more than half a century, the methods and the instrumentation are still being refinedin order to minimize their uncertainty, to extend their frequency ranges, to include extraparameters and to speed up slow processes. In addition to the traditional methods formicrophone sensitivity and frequency response calibration, new development areas, like forexample wind power, has created needs for low-frequency and infra-sound calibration, downto 0.1 Hz. Other high-tech areas have lead to the development of methods for phaseresponse comparison calibration of microphones for large arrays, for sound intensitymeasurement and for verification of dynamic linearity of microphones at very high soundpressure levels, up to about 174 dB that corresponds to 10 kPa.