What do professors do with personal copies of old textbooks? I've been teaching a few years now and the number of older editions of textbooks is beginning to pile up in my office. There is no policy at my university for disposal of old textbooks. These books were purchase with department funds and it troubles me to throw them away. They content is still relevant as the newer editions are not ground-breaking in material.

My questions are as follows...


Please share how you deal with older editions of textbooks? 
Is there a policy at your institution (if so please share) or do you have a personal way of dealing with this problem (again please share)?
At my school the custom seems to be just leaving them in a stack in the hallway next to one's office door. Anyone walking by can peruse through them and take anything they want. At some point the janitorial stuff disposes of the stack as rubbish.