Five refractive methods and an interferometric method for measuring refractive indices of optical glasses to a precision of several units in the sixth or seventh decimal place are examined. Tables and graphs are presented as aids in evaluating the various methods. Reduction to standard conditions of temperature, pressure, and humidity is also discussed. The minimum deviation method provides greater precision than the autocollimating method for the same precision in angle measurement. The V block, immersion, and critical angle methods, being comparative methods, provide lower precision. A proposed interferometer method shows capability for seventh place accuracy.