A postdoctoral (colloquially, "post-doc") appointment is a usually temporary academic job held by a person who has completed his or her doctoral studies. Postdoctoral appointments commonly last for periods ranging between six months and three years, and are usually oriented more toward research than teaching. The appointee is usually given the title of research assistant or fellow.

Before entering certain fields, a post-doc appointment may be a necessary step in order to gain greater knowledge and experience, make connections, and build a name for oneself in research circles. It may also be seen as a valuable tool to distinguish oneself from other candidates when entering the job market. Such appointments are often the "stepping stone" whereby a graduate student can improve his or her publication record and hence progress to a permanent academic post.

In many academic fields, post-doctoral appointments — traditionally optional — have become mandatory as tenure-track positions are simply unavailable for those who have not completed post-doctoral or adjunct positions. Without post-doctoral experience, most fresh doctorates lack the connections and prominence needed to secure a better academic job.

As the doctorate degree is, by definition, the highest awarded in a field, no degree is given at the completion of a post-doctorate position. Some postdoctorate positions share more in common with low-paid adjunct jobs than continuing education. In some fields in some countries there are so many graduates that post-doctoral work is almost necessary. In some situations academics sometimes take second and third post-doctoral positions.