By using a multiphase detection technique, unambiguous shot-noise-limited measurements of unwrapped (i.e. not limited to modulo 21) interferometric phase may be made at data rates in excess of 1 MHz. This technique is ideally suited for use with laser diodes. We describe the technique and associated algorithms which facilitate the rapid processing of data, and we present experimental data obtained with different types of laser diode interferometers--including an imaging interferometer in which phase is digitally measured for each pixel at TV frame rates, and an interferometric linear encoder head which achieves a 1-microinch resolution with a 1250 line/inch linear scale and a 1 MHz update rate.