The document summarizes lessons learned from the first 20 years of open source software. In the first decade (1998-2008), open source advocacy and standardization of licensing through the Open Source Initiative helped drive adoption. The second decade (2008-2018) saw broad enterprise adoption as open source powered cloud, web services, and became central to most new software. Key lessons included how open source licensing crystallized consensus, created safe development spaces, and isolation of business models from code. Future challenges include license compliance, attribution requirements, and integrating open source values with standards as different industries converge.