Measurements now being made with the aid of lasers cover a broad range of scientific problems. The most unique new capability is precise distance measurement over ranges of many meters using the stable wavelength of the laser light as a resolution limit. This falls in the category of inter-ferometry and has been covered very well by Herriott (Ref. 1). The laser has also become very useful for measuring long ranges with high relative precision but with resolution considerately less than that of the light wavelength itself. There are a number of ways to use the laser frequency as a carrier of much lower frequency information. This yields another kind of interferometry which uses "fringe" detectors that are quite different physically from the mirror interferometers used for very precise measurements. But the detectors for modulations put on laser light are true interferometers also, and merely work at a much longer wavelength. These techniques yield lower absolute resolution, but still give very meaningful and useful measurements with high precision when necessary.