Harvard University offers a wide range of challenging and rigorous degree programs across various disciplines, so it is difficult to determine definitively which degree is the hardest to earn. The difficulty of a degree program can depend on various factors, including the subject matter, the individual student’s strengths and interests, the program’s requirements, and the level of commitment and effort put into the studies.

That being said, some of the programs at Harvard that are widely regarded as academically demanding and highly competitive include:

1. Harvard Medical School (Doctor of Medicine): The medical program at Harvard is renowned for its rigorous curriculum, extensive clinical training, and high standards of academic excellence. It requires several years of intense study, clinical rotations, and demanding exams.

1. Department of Mathematics (Ph.D. in Mathematics): Harvard’s mathematics program is known for its emphasis on theoretical and abstract mathematics. The program requires a deep understanding of advanced mathematical concepts and rigorous proof-based problem-solving.

1. John A. Paulson School of Engineering and Applied Sciences (Ph.D. in Engineering or Applied Sciences): The engineering and applied sciences programs at Harvard involve challenging coursework, research projects, and often require strong quantitative and analytical skills.

1. Department of Physics (Ph.D. in Physics): Harvard’s physics program is highly regarded, and it covers advanced topics in theoretical and experimental physics. It requires a solid foundation in mathematics, a deep understanding of fundamental physical principles, and the ability to conduct complex experiments.

1. Harvard Law School (Juris Doctor): The law program at Harvard Law School is known for its rigorous curriculum, high academic standards, and competitive admissions process. It involves extensive legal research, analysis, and writing, as well as a challenging workload.

These examples are not exhaustive, and the difficulty of a program can vary depending on individual factors. Additionally, it’s important to remember that each student’s experience and perception of difficulty may differ. What may be challenging for one person could be an area of strength for another.