Every entrepreneur has one thing in common: too much free time. Day in and day out, CEOs, presidents and the like all seem to sit around twiddling their thumbs. Just kidding! But if you’re an entrepreneur and you do somehow find yourself with a spare moment to breathe, I say you crack open a book. Countless books can teach you valuable lessons about running your own business, interacting with customers and optimizing sales. Some impart professional wisdom without even being about business. Here are the types of books every entrepreneur should read:

1. Books Written By And About Successful Businesspeople

Who better to get advice from than someone who’s already done what you want to do? If you want to found and operate a successful business, learn about how others did the same. The books can be about successful entrepreneurs or just good businesspeople. And while business changes over time, remember you can always learn from entrepreneurs of the past. Here are a few examples:

• The Autobiography of Benjamin Franklin, by Benjamin Franklin. Franklin is often considered America’s first true entrepreneur, so there’s plenty to learn from his life. The founding father offers advice in his book, including a step-by-step plan to achieve “moral perfection.”
• Titan: The Life of John D. Rockefeller, Sr., by Ron Chernow. Rockefeller’s business success earned him the title of the world’s first billionaire, and this book shows how it all happened. The description says it’s “the first full-length biography based on unrestricted access to Rockefeller’s exceptionally rich trove of papers.”
• Steve Jobs, by Walter Isaacson. This book is about the life of Apple cofounder Steve Jobs, one of the most successful entrepreneurs of recent times.
• The Road Ahead, by Bill Gates. Gates’ life is another modern success story, and his book tells of his industry. It focuses on the personal computing revolution and how computers became mainstream. It sounds a bit dated, but still gives insight into Gates’ thought processes.

2. Books Read By Successful Businesspeople

You’ve gotten advice from your mentors; now get advice from their mentors. Many successful businesspeople recommend books to their fans, so it’s easy to find out what your favorite entrepreneurs are reading. Here are some big names and what they recommend:

• Oprah Winfrey is always updating her reading list, but the materials aren’t always applicable to running a business. She did come up with a list in 2010 of the 10 books that mattered most to her in the last decade, some of which focus on how to optimize your life.
• Amazon CEO Jeff Bezos has three book recommendations for businesspeople. He likes them so much that they were recently required reading for his top executives. They include The Effective Executive by Peter Drucker, The Innovator’s Dilemma by Clayton Christensen, and The Goal: A Process of Ongoing Improvement by Eliyahu M. Goldratt and Jeff Cox. Remains Of The Day Is on of his favorite books.
• Bill Gates released his summer reading list, which included some books he’s already read as well as some he’s looking forward to reading. It included some books about success (like How Children Succeed by Paul Tough), some about life (like Whistling Vivaldi: How Stereotypes Affect Us and What We Can Do (Issues of Our Time) by Claude Steele), and some that he just found interesting.

3. Books About Your Type Of Business

You should always stay on top of what’s going on in your industry. If you’re an app developer, read books pertaining to the newest technology; if you sell paper, see if Michael Scott from Dunder Mifflin has a book coming out. It seems like a no-brainer, but it’s important to know how your specific industry is operating and adapting.

4. Books About Other Types Of Business

It’s also important to learn about industries you’re not directly involved in, especially when it comes to technology. Every good entrepreneur should make an effort to keep up with technology and branch out in any way possible. Read about computer programming, social media, advertising and anything else you can think of. Learn about every tool out there, and then start utilizing everything at your disposal. When in doubt, you can always pick up a For Dummies book to get you started.

5. Books That Aren’t About Business At All

You may have gathered from Oprah’s, Bezos’ and Gates’ suggestions that books don’t have to be about business to be directly or indirectly applicable to your work. The Art of War by Sun Tzu, for example, is a book commonly recommended for salespeople. The ancient book is about actual war but gives advice that’s equally applicable on the sales floor, as long as you want to treat potential customers as enemies. Whatever you read, try to take lessons away from it that you can use toward your business.

6. Books You’ll Enjoy

There’s no hidden message behind this one, and there’s no lesson to be learned. Sometimes you just want to kick back with a good book and get lost in a different world. Forget about your own business for a bit and relax a little. Pick up a Harry Potter book or War and Peace, as long as you enjoy it.