It really depends where you want to work. Gonna make some wild guesses here! 1. SV startup: Python, Ruby are best bets. Java will make people squirm. C# will m

It really depends where you want to work. Gonna make some wild guesses here! 1. SV startup: Python, Ruby are best bets. Java will make people squirm. C# will make people tilt their heads. You'll probably get bonus points for Go 2. Google/Microsoft/Amazon: If you know C or C++ you'll be fine. 3. Facebook: They really let you interview in anything but you might as well be awesome in PHP. That said, they definitely use other languages internally. 4. Other: Java. If the company uses C#, they'll still probably be OK with you only knowing Java. At a certain point, companies shouldn't be hiring for languages you know since a language can be learned relatively easily compared to the Larger Broader Concepts that they should really be trying to probe for. Which is generally true - any company who doesn't give you an offer because you didn't memorize language syntax for whiteboarding is crazy. It's not about that. What it is about (I think) is trying to figure out who are you?. As an example, if you only know Java many people will think "oh this is your run of the mill CS student who doesn't do side projects" - whether true or not (of course it's possible to do side projects in Java). But it just makes people think you have less initiative than the applicant next to you that knows Java (because he has to) but also knows Python (because he wants to)