While law professors have traditionally had only law degrees, a growing percentage have PhDs in addition to or instead of JDs.

Almost all professors in law schools have a law degree.  Traditionally, this was the only academic credential necessary for teaching in law schools, but in the last decade or so, a growing percentage of law professors have PhDs in addition to or instead of JDs—about 25% of professors at the most selective law schools. (Some may have LLMs – a master’s degree in law – or, more rarely, JSDs – a doctorate of law). 

For teaching law in four-year undergraduate liberal arts institutions, however, a JD is generally insufficient.  Almost all such professors have PhDs, most often in the social sciences.  Among professors in law-related pre-professional programs (such as paralegal certification programs) or in community colleges, JDs (without a PhD) are more common.