Students must petition the Committee on Higher Degrees for permission to register on Leave of Absence or as a Traveling Scholar. Traveling Scholar is appropriate for students who are doing degree-related work, but away from Cambridge. Those students may get a non-resident student ID card through the registrar's office, and may also get a formal letter of introduction from the Dean's Office in Byerly Hall. In this registration category, the clock keeps ticking toward the five-year deadline for the Ph.D.
Leave of Absence is the appropriate registration category for students not doing degree work. In this category, the clock stops; upon return, a student called "G4" by the graduate school will actually be treated by the Department as a G3. For students in good standing, Leave of Absence is approved fairly automatically in cases where there are medical requirements (ill health, hospitalization, etc.), parental responsibilities, or situations where personal circumstances require the student to take a temporary absence from graduate school: moving with a spouse away from Cambridge, for example. The CHD will normally not allow a leave for students who simply want to "recharge their batteries," or who are not in good standing.
The Department will not pay financial aid while a student is on leave. The minimum possible tuition payment to remain on the books is the Active File Fee (about $250). Paying this fee does not remove the obligation to pay two years full and two years reduced tuition--it simply delays it (if those payments haven't already been made). Students wishing to retain Harvard student health insurance must pay at least the facilities fee. A student on leave to attend another Harvard graduate school is exempt from any tuition.
Students are not normally allowed more than one year of Leave of Absence before completion of general exams. A student who withdraws in the G1 year, for example, will not typically be allowed a second year of Leave. The student must instead withdraw from graduate school, and reapply for admission during the normal admissions season when they wish to return. Their application will be judged along with all other applicants, so there is no guarantee of readmission.
More information about leave can be obtained from Rise Shepsle, the Student Affairs Officer in the Dean's Office, 495-1816. Leave forms are available in the Graduate Office.
Students who withdraw from graduate school because of the five-year rule are more-or-less automatically readmitted when they finish their thesis. Readmission forms can be requested from the Student Affairs Officer. There are no firm deadlines for this readmission (other than that it happen before graduation), so students are advised to make sure their thesis committee agrees that they are ready to defend the thesis before they request readmission. Before graduation, such students must pay the Active File Fee for each semester they were withdrawn (currently $125/semester), and the Facilities Fee for the semester in which they receive the diploma.