Problem-based learning (PBL) is an instructional strategy of "active learning" often used in higher education in such fields as nursing, dentistry and agriculture. The modern history of PBL began at the medical school at McMaster University where Howard Barrows pioneered its use in response to the poor knowledge base that medical students accrued during their neurology clinical residencies. However, its intellectual history can be traced back through inquiry training, John Dewey, and student apprenticeships.