Many of the kernel developers are paid for their efforts by somebody, yes. Red Hat is the top single corporate employer, but their contributions are roughly 12%

Many of the kernel developers are paid for their efforts by somebody, yes. Red Hat is the top single corporate employer, but their contributions are roughly 12%: http://www.linuxfoundation.org/sites/main/files/publications/whowriteslinux.pdf http://www.linuxfoundation.org/sites/main/files/publications... From Red Hat's point of view, even though someone else is typically paying for the effort, code that's not from their developers is "free." (Well, Red Hat is also one of the top reviewers, so they're paying people to review the contributions of others, too. So it's a bit more complicated than that.) Now, some of the companies on that list are in the same business as Red Hat (and some companies are in the same business but don't contribute significantly to the kernel, like Canonical). But many of them are in very different lines of business and view the Linux kernel as either a complement (that's why Intel is involved, for instance -- encouraging free operating systems to sell processors) or as an infrastructure piece for their products (yo, Google). So Red Hat is able to leverage the efforts of those companies to deliver a product for far, far fewer man hours than it would cost if they did all the work themselves.