Bill Gates is one of the smartest men in the world. But when he reads for pleasure, he likes books that make him feel dumb. 

In a post on his personal blog, The Gates Notes, the Microsoft founder explained the books he gravitated to this year. Contrary to what you'd expect, they had nothing to do with computers and everything to do with topics ranging from the environment to how the economy works. While he clearly prefers nonfiction, he made sure to reread one of his favorites, J.D. Salinger's The Catcher in the Rye

Reading is crucial to becoming a smart entrepreneur. It broadens your mind, improves your social skills, and if you're savvy like Gates, gives you grist to sell people on your business or idea. Here's a look at four surprising books that made Gates's reading list.

Harvesting the Biosphere by Vaclav Smil 

The Czech-Canadian scientist has made a name for himself bringing together disparate topics like technical innovation and nutrition into his research. "There is no author whose books I look forward to more than Vaclav Smil," writes Gates. While he admits the book is "dry," the challenge of looking up a number of unfamiliar terms helped him better understand how humans are reshaping the environment.

Poor Numbers by Morten Jerven

Is it time to invest in better GDP statistics? Jerven, an economist, thinks so, having researched how African nations come about their statistics. Estimates of economic growth and per capita income are vital to nongovernmental organizations, but many of them are inaccurate, writes Jerven. Gates isn't convinced the African stats are entirely useless, but says the book offers insight into the changes that need to be made.  

Why Does College Cost So Much? by Robert B. Archibald and David H. Feldman

Gates offers a rather simplistic view of the problem: "As long as there's a scarcity of college graduates, a college degree will be quite valuable," he writes. "So people will pay more to get one." The authors lay out a number of policies that might help reverse the trend. The main takeaway is that the system is inefficient and some schools could stand to be consolidated, especially in Chicago. 

The Bet by Paul Sabin

Is the world headed for environmental catastrophe? This topic is near and dear to Gates, who's famously backed climate scientists lobbying for large-scale geo-engineering in the past. The story centers on Paul Ehrlich and Julian Simon, who wagered $1,000 that overpopulation and the depletion of resources would only worsen with time. The conflict that ensued between ecologists and economists was a riveting read.