Important information on the dissertation is to be found at the GSAS Dissertation Website, including a "Dissertation Tool Kit." All PhD students should regularly consult this site, which gives dates of all relevant deadline as well as forms to be completed.
Every PhD dissertation at Columbia will have a primary Faculty Advisor (a duty sometimes shared between two faculty members) and a total of five readers. Three of these, including the Faculty Advisor, normally come from inside the department, two from outside (either at Columbia outside the department, or outside Columbia, from another university). Normally the three inside members are the same as those who conducted the dissertation prospectus defense, but often the composition of the committee will change after prospectus defense.
The Faculty Advisor (or first reader) will work closely with you throughout the writing, shaping, and revising of the dissertation in its successive drafts. The second reader also reads the dissertation in draft form and confers with you prior to distribution of the dissertation. The third reader is available to you for occasional consultation, but his or her work as reader does not normally begin until the dissertation is approved by the first two readers. When the subject matter of your dissertation overlaps with another discipline, you may find it profitable to check your work, or portions of it, with a scholar in that field, whether or not he or she is one of your readers.
The doctoral defense is your final examination. You will be expected to answer questions related directly to your dissertation. Defenses are oral, last about two hours, and usually take place in one of the seminar rooms in Dodge Hall.