This position is generally taken after earning a doctoral degree and generally after several years of holding one or more postdoctoral researcher positions. It is below the position of associate professor at most universities and is equivalent to the rank of lecturer at most Commonwealth universities. In the United States, assistant professor is often the first position held in a tenure track, although it can also be a non-tenure track position. Full professorships are assistant professor, associate professor, and full professor in order. After 7 years, if a tenure-track position and successful, if not tenured, in the U.S. assistant professors can get tenure and are traditionally promoted to associate professors. It is very competitive to become a tenure-track assistant professor, especially at top tier and research universities in the U.S., U.K. and Sweden. Often hundreds of applicants apply for a single position. Due to funding issues the number of positions for full time professors (either assistant or associate) has dropped significantly. Colleges are saving money by replacing full-time professors with adjuncts. With these facts, less than 20% of graduates get tenure-track assistant professor positions after graduation.
The table presents a broad overview of the traditional main systems, but there are universities which use a combination of those systems or other titles. Some universities in Commonwealth countries have also entirely adopted the North American system in place of the Commonwealth system.