Two methods for the accurate determination of high vacuum pressure are reviewed with particular attention paid to the 10\sp−6 to 10\sp−5 Torr range. The first method is characterized by calculating the pressure generated from a knowledge of the characteristics and geometry of the vacuum chamber. Static and dynamic expansion techniques are examined. The second method establishes a pressure in the vacuum chamber by balancing an input of gas against a pumping speed and measuring the resulting pressure with a suitable gauge. McLeod, spinning rotor, hot-filament ion, and capacitance diaphragm gauges are discussed. Additionally, new results for ion and capacitance diaphragm gauges are presented including an extension of the range of capacitance diaphragm gauges down to 10\sp−6 Torr through the use of averaging and a new technique for the direct calibration of capacitance diaphragm gauges between 10\sp−6 and 10\sp−4 Torr which uses gravity to deflect the diaphragm and generate apparent pressures.