There are quite a few suggestions online for selling, giving away or otherwise disposing of no-longer-needed books from our personal libraries, but here a few of my own suggestions.
I confess to being a book collector. Not only do I tend to purchase books about my hobbies and interests, but each time I have taught a course or given a lecture, I also purchased a number of books about the topic, especially since the local libraries do not have the books ready to hand that I need. Moreover, the last two times I moved from one parish to another I barely had a week's notice. The first time I dragged all my books with me, the second time I donated many to the parish library and threw a great number in the trash (mea culpa).
So, snowed in and surrounded by books, I decided to approach my collection in an orderly manner. Donations to our school library and the nucleus of a parish resource library in the St. Michael Media Room was the first step. Next, I put aside books I refer to frequently or anticipate using within the next few months/years for projects, interests or pleasure reading including some classics. I decided to be pretty stringent with these criteria. That left a lot of now unwanted books.
For example, after ordination, I began buying books on sacred art and for a few years photographed the art for 35mm slides (remember them?). At first very slowly and then almost explosively, high quality digital images of artwork became available on the Internet. So, no more lights, cameras or art books necessary...just lots of heavy, hard-to-move art books.
For each remaining book I asked: How much is it worth? A handheld scanner made answering this question easy. I scanned in the barcode and consulted bookscouter.com for vendors likely to buy the book. Many were worth several dollars, some several cents, many more worth nothing. I put aside those worth several dollars or more for selling on the used book market. If the book were worth nothing or very little on the used market, would any parishioner likely be interested in reading it or would it be worthwhile in the parish library and is it in good condition? If so, I added it to the donation pile. If not, the paperbacks were sent to recycling and after the hardcovers were removed from the others, so were their contents.
The used book vendors will acknolwedge your order and price your books before you ship them. Shipping labels and packing lists can be printed from your home computer. USPS and FedEx were the most commonly used carriers. All shipping is free. Packing, sealing and shipping the books isn't easy, but at least some of their worth is recovered and the idea that someone may actually still use the books made it a bit easier for me to discard them.
Packing and shipping the books isn't the hardest part though. Anytime we sort through any of our possessions, we are forced to ask difficult questions about ourselves. Why am I keeping this? Why did I acquire it in the first place? If I haven't read this yet, will I ever? Where I am likely to move next, remembering you don't get to take anything with you on the last really big move.
I consoled myself that if I ever need any of my old friends again, I can visit with them digitally. It's a lot easier to move around a Kindle than 20 cartons of books. I won't tell you what I did with my VHS tapes!