A report from the Linux Foundation addressing Who Writes Linux (2013) shows that recent releases of the Linux kernel, that happen now at 70-days intervals, include over 10,000 patches, made by more than 1,100 developers, representing over 225 corporations.
Since April 2012, when the previous report was published, almost 92,000 changesets have been merged from 3,738 individual developers representing about 536 corporations, adding close to 2 million lines of code. Cumulatively, the Linux kernel has been the work of more than 11,000 developers collaborating for more than 20 years.