An assistant professor is an academic rank used in universities or colleges, mainly in the United States, Canada, Japan, and South Korea. It is an entry-level university teaching position below that of associate professor and full professor. The position is generally taken after earning a doctoral degree and after several years of holding one or more postdoctoral researcher positions. Assistant professor is often the first position held in a tenure track, although it can also be a non-tenure track position. The typical professorship sequence is assistant professor, associate professor, and full professor in order. After seven years, if successful, assistant professors can get tenure and also get promotion to associate professor.

The responsibilities of an assistant professor include teaching a requisite number of classes, providing guidance and supervision to graduate students, participating in departmental meetings, and providing academic support to professors and other faculty members. They also conduct research and publish papers in academic journals, represent the university at conferences, and deliver presentations when necessary. Additionally, they recruit, train, and mentor new TAs and other junior staff.

Less than 20% of doctoral graduates move onto a tenure-track assistant professor position after graduation. There is high demand for vacant tenure-track assistant professor positions, often with hundreds of applicants.