Linux Kernel Development: How Fast it is Going, Who is Doing It, What They are Doing, and Who is Sponsoring It 
The kernel which forms the core of the Linux system is the result of one of the largest cooperative software projects ever attempted.
Regular 2-3 month releases deliver stable updates to Linux users, each with significant new features, added device support, and improved performance. The rate of change in the kernel is high and increasing, with over 10,000 patches going into each recent kernel release. Each of these releases contains the work of over 1,400 developers representing over 200 corporations.
Since 2005, some 11,800 individual developers from nearly 1,200 different companies have contributed to the kernel. The Linux kernel, thus, has become a common resource developed on a massive scale by companies which are fierce competitors in other areas.
This is the sixth in a series of regular updates to this document, which has been published roughly annually since 2008. It covers development through the 3.18 release (which came out on December 7, 2014), with an emphasis on the releases 3.11 to 3.18. It was a typically busy period, with eight kernel releases created, many significant changes made, and continual growth of the kernel developer and user communities.