In his book The Wealth of Networks (2006), Benkler significantly expands on his definition of commons-based peer production. According to Benkler, what distinguishes commons-based production is that it doesn't rely upon or propagate proprietary knowledge: "The inputs and outputs of the process are shared, freely or conditionally, in an institutional form that leaves them equally available for all to use as they choose at their individual discretion." To ensure that the knowledge generated is available for free use, commons-based projects are often shared under an open license.