I consider myself a pretty eclectic reader. I enjoy books on psychology, philosophy, self-help, writing, communication skills, politics, relationships, history, marketing, business, science, and religion. Anything that presents a unique yet elegant point of view on a topic.
Despite this variety, however, one thing I've noticed is that in different periods of my life, I find myself returning to the same few books. (See the 80/20 principle.) Some books explore concepts, ideas, principles that just stick with me more than other books.
These books have shaped the way I think about something, allowing me to carry their ideas and sentiments and influence how I live. They aren't simply interesting and thought-provoking – they are life-changing.
I call these types of books “the essential library” – that small collection of books that you return to often for wisdom and/or that deeply shape your thinking. These books are essential because without them, you wouldn't be the person you are today.
(Site note: essential libraries are essentially the opposite of what Nassim Taleb calls the anti-library – those books that you have not read, but may read in the future for research purposes. However, the idea is the same: you're not collecting these books to show off, but to actually use them.)
The idea is to keep this library as small as possible, by applying two simple criteria when considering a book:
If it passes that test, then it deserves to be put in my essential library.