On November 3, 2007, six vehicles made history by successfully navigating a simulated urban environment—and complying with California traffic laws—without a driver behind the wheel. Five of the six were sporting a revolutionary new type of lidar sensor that had recently been introduced by an audio equipment maker called Velodyne.

A decade later, Velodyne’s lidar continues to be a crucial technology for self-driving cars. Lidar costs are coming down but are still fairly expensive. Velodyne and a swarm of startups are trying to change that.

In this article, we’ll take a deep dive into lidar technology. We’ll explain how the technology works and the challenges technologists face as they try to build lidar sensors that meet the demanding requirements for commercial self-driving cars.