Internal transfers

Between CC and SEAS

Students rarely transfer from SEAS to CC, but it's nevertheless possible.

Between CC/SEAS and GS

If you drop out and aren't allowed back as a CC/SEAS student, you may be able to return via GS. There is apparently a procedure for transferring from GS to CC/SEAS but there are no documented cases of this occurring.

Between CC/SEAS and Barnard

Haven't heard of any cases.