The Institute of Astronomy offers the opportunity to study for the PhD degree, for which the normal duration of study is expected to be three years. The format is almost exclusively research based, although students during their first two years attend a number of specialist courses on current research topics given by members of the Institute of Astronomy and Cavendish Astrophysics. PhD projects may be exclusively theoretical or observational but many combine aspects of both. It is normal for students to attend at least one relevant international conference during their three years of study, and most students working on observational research projects will normally undertake a number of observing trips (depending on the requirements of their project) to telescopes overseas. There is an induction programme, and a series of Graduate Lecture Courses, which students must attend. Training is given on observational and computational techniques and presentation skills. The degree of PhD is awarded primarily on the quality of a dissertation of not more than 60,000 words constituting a substantial contribution to original research. The thesis is assessed critically by two examiners who then conduct an oral examination upon the subject of the thesis and the general field within which it falls.