At the lower levels, Uber’s engineers primarily write in Python, Node.js, Go, and Java. We started with two main languages: Node.js for the Marketplace team, and Python for everyone else. These first languages still power most services running at Uber today.

We adopted Go and Java for high performance reasons. We provide first-class support for these languages. Java takes advantage of the open source ecosystem and integrates with external technologies, like Hadoop and other analytics tools. Go gives us efficiency, simplicity, and runtime speed.

We rip out and replace older Python code as we break up the original code base into microservices. An asynchronous programming model gives us better throughput. We use Tornado with Python, but Go’s native support for concurrency is ideal for most new performance-critical services.

We write tools in C and C++ when it’s necessary (like for high-efficiency, high-speed code at the system level). We use software that’s written in those languages—HAProxy, for example—but for the most part, we don’t actually work in them.

And, of course, those working at the top of the stack write in languages beyond Java, Go, Python, and Node.