The open source model, initially spawned by anti-proprietary ideology, was adopted by the software industry as a viable alternative to proprietary software. Along with the open source paradigm, commercial firms also adopted the GPL, a restrictive license that manifested the core objectives of the Free Software Foundation (FSF). Ostensibly, even if a license is not optimal, the contribution of this understanding remains at the theoretical level, as commercial firms are free to choose any licensing structure they wish, including licenses that are not socially optimal. However, the special nature of copyright law, coupled with the major role of the FSF in the open source arena in general and specifically in the enforcement of the GPL, significantly transforms the picture. The FSF, almost akin to a legislator, has both the tools and the public standing to implement changes if the GPL were not to be socially optimal and if another approach could alleviate its inefficiencies and still be consonant with maintaining the underlying goals of the GPL. This dissertation offers a comprehensive methodology that provides a deep understanding of the open source model and copyleft licenses under the current copyright law. I analyze the GPL from four different perspectives: incentive, information costs, enforcement and access to knowledge. For each angle, the analysis first explores both the strengths and the weaknesses of the copyleft license, then examines the implications, and lastly explores whether the market mechanisms support the evolvement of efficient solutions. The dissertation suggests that the GPL, along with other open source licenses, has an important role to play in the current intellectual property regime - a role that is effectively executed by commercial firms that have warmly adopted the open source model. However, both the GPL and BSD licenses fail to maximize the benefits of the open source paradigm where it could best manifest its superiority over the proprietary regime: in the area of intangible 'foundation products‘, i.e., goods that do not have a discrete value in of themselves and whose value is in subsequent goods. To this purpose, neither the GPL nor the BSD license is optimal. To maximize the superiority of open source software where it is most needed, I outline specific principles for a more efficient licensing structure. The analysis also suggests that the inefficiencies of the copyleft regime evinced when applied to the software industry could be frivolous when used with other copyright subject matter.