Friends and readers periodically ask, especially given the volume some months.

Here's the answer:

1.  I don't sell any of them.

2.  I keep a quarter to a third of them for my own reading.  A number of these books were really important to my work, so I am grateful for the windfall of getting complimentary copies.

3.  I have a stack of books in my office which I invite students and colleagues and other visitors to take if they are interested in the subject.  That accounts for about half.

4.  I give the rest to the university library.