One option, when space is an issue, is to completely discard the physical book collection and buy an e-reader. This option doesn’t work for everyone though. First, replacing all existing volumes can get pricey even though many titles are free or minimally priced. But more importantly, e-readers don’t work for people like me, people who are technologically-challenged (I have issues with my vacuum), people who have a low tolerance for gadgetry, electronics, and technology. The physical sensations of reading a book cannot be replaced by hard metal and cold plastic. I love the feel of old pages, the texture of old covers, the slightly musty fragrance of old volumes. Curling up in bed with a good e-reader is just not the same. As I turn the pages of an old volume I think about all the other folks who have read it before me; it’s a bond of shared experience and shared enjoyment with nameless, faceless individuals that I’ll never meet; a link with humanity that lets me know I’m not alone in my appreciation. I also enjoy the homey feel books can give to a room. Books are a form of self-expression, a manifestation of what I like, what I’m interested in, and what I have passion for. A bookcase is one of the easiest ways to express yourself in your home.
Consider an e-reader to replace some or all of your books. If you’ve never tried one, many local libraries offer e-readers that can be checked-out. Try it on for size. They work well for many people and certainly solve the space issue.