My dissertation looks at the Governance Structures of Free/Open Source (FOSS) Development, based on a case study of FreeBSD, a large FOSS project. More specifically, it examines 3 well-known theories. The 1st theory [decreasing returns to scale] holds that increasing the number of persons working together results in a productivity drop due to (a) increased coordination costs and (b) reduced individual motivation. The 2nd theory [iron law of oligarchy] holds that a group's ability to self-organise diminishes as it gets larger, thus necessitating hierarchical coordination. And the 3rd theory [modularity theory] holds that modularity (a design principle implemented by breaking down a product into autonomous components) increases the potential number of persons working on a distributed project and has a positive effect on their labour productivity, because it allows them to work independently of each other, with little or no need for active coordination. To test these theories, we looked at the development of the FreeBSD operating system project over a period of 15 years, in which time the number of persons developing it increased dramatically from about a dozen in 1993 to several hundred in 2010. What we found, with respect to the 1st theory, is that indeed the increase of FreeBSD developers resulted in a fall in group performance but the cause of this was the disproportionate increase of 'lower-contribution' participants over time, and not increased coordination costs or reduced individual motivation. With respect to the 2nd theory, we ascertained that the increase of scale of the FreeBSD group in numbers did not result in hierarchy, which outcome is accounted for by the normative standard of individual autonomy of action and the fact that the distributed environment in which FOSS projects operate does not foster hierarchy. With respect to the 3rd theory, we found that indeed modularity increases the potential number of persons working on a project and has a positive effect on their performance, as it allows them to work independently of each other, with little or no need for active coordination.