  First observations for the Parkes Pulsar Timing Array project were carried
out in February 2004. The project is ongoing and we currently observe
approximately every three weeks. The data have led to numerous scientific
results on topics as diverse as the solar wind, gravitational waves, measuring
the masses of planetary systems in our solar system, atomic time scales, the
interstellar medium and the pulsar emission mechanism. In this paper we provide
an historical overview of the project and highlight the major discoveries.
