Listing programming languages is easy—Wikipedia's page has more than 600 entries—but ranking them by popularity is hard. As David Welton, curator of the site LangPop.com, points out, you can't send out a horde of researchers to look over programmers' shoulders and note what languages they're coding in. So you have to get at it indirectly.
To do that, you can search the Web and find numbers to use as a proxy. And you can tailor the search to target different kinds of popularity: Which languages are the most sought after in the job market? Check a job site. Which are used by elite programmers? Look in on their chat sessions. How established is a language? Visit an online bookstore—new and esoteric languages don't have many reference books dedicated to them.
The data here come in part from TIOBE, a software research firm based in Eindhoven, Netherlands. The analysts there produce an aggregate index each month. I also looked at Welton's LangPop.com, which shows the results of individual searches, such as on Craigslist, Internet Relay Chat, and Powell's Books.
Generally speaking, the languages being talked about by programmers online aren't quite the same as the ones at the top of the TIOBE Index or those that have spawned a lot of book titles (C++ is an exception). The most sought after by employers seem to be PHP, a language used in Web development, and SQL, which is used for writing database queries. No surprises there.
And then there's Objective-C, which underlies Mac OS and iOS and was barely in TIOBE's top 40 in 2008. But since then, it's climbed rapidly in popularity because people have been using it to write apps for the iPhone and iPad.
About the Author
Ritchie S. King formerly dealt with numbers full-time as a chemical process engineer. Unlike most engineers, though, he enjoyed writing reports and making charts more than any other aspect of the job. In 2009, King decided to make writing about science and technology a full-time gig. He landed an internship at Spectrum this past summer and is currently finishing journalism grad school and interning at The New York Times.