The Hipparcos and Tycho Catalogues were published in 1997. In the intervening 10 years, several thousand papers making more-or-less direct use of the data have been published. I summarise a number of scientific applications which illustrate the variety of problems to which the data have been applied. This includes the re-reduction of old and contemporary astrometric observations, investigations of Galactic structure and dynamics, investigations of stellar structure and evolution, investigations of the Solar System and our Earth's environment, and various uses of the binary star and photometric data.