If you are looking for dissertations in general, use ProQuest and search their comprehensive collection. You can search Digital Dissertations by a number of fields, including, but not limited to: Abstract, Advisor, Author, Citation, Degree, Department, Index Terms (Keywords), School, and Subject.
If you are looking for Teachers College dissertations specifically:
Teachers College Ed.D.s up through 1996 are digitized and archived in PocketKnowledge. After 1996, they are available through Digital Dissertations. If you click on Dissertations from TC, your search will be automatically limited to Teacher College Ed.D.s (but not Ph.D.s).
Teachers College Ph.D.s before 1996 are not yet digitized for archival in PocketKnowledge. TC Ph.D.s after 1996 can be found digitized through Digital Dissertations.
Note: Teachers College Ph.D.s are assigned to Columbia University in Digital Dissertations. So, if you are searching by school for a TC Ph.D., enter Columbia University in the school field.
Hard copies of Teachers College Ed.D.s and Ph.D.s are available at the library. To search EDUCAT for a dissertation, click on the link that says “Limit EDUCAT to… Dissertations,” and then proceed with your search as usual.
Most dissertations are located in the closed stacks. You may place a request online or in person at the circulation desk for their retrieval.
You can also browse through very recent dissertations which are displayed on the third floor of the library.