Within the last 25 years, the precision with which many physical measurements can be made has increased dramatically. The place of measurement in establishing physical ideas is considered and examples of the use of very precise measurements in fundamental studies are given. Modern engineering is largely dependent on accurate, convenient measurements in design, construction and communication, and modern measurements depend on quantum standards of frequency, wavelength, voltage and others. The very precise measurements that these techniques make possible have many applications; examples arc taken from the study of the structure of matter, from geophysics and astronomy.