You can become a Deputy Borrower at the Gottesman Libraries at Teachers College by bringing a letter signed by your supervisor to the 1st Floor Information Desk of the library.

The letter must stipulate the length of time (usually one semester) that you will function as a deputy.

The letter must include the following information for both supervisor and deputy:

Full Name
Campus Address
Campus Telephone
Home Address
Home Telephone
ID# from Back of ID 

All items borrowed on the Deputy Borrower account become the sole responsibility of the Faculty Member or Administrator. 

A student cannot be a Deputy Borrower for another student.

Teachers College faculty who wish to deputize someone to manage their Course Reserves can do so here

Becoming a Deputy Borrower at the Columbia University Libraries is a separate process. See how here.