Science, technology, engineering, and math (STEM) education have become a priority for nations around the world, yet many students – in both developing and developed countries – lack access to high quality STEM learning experiences. For 17 years, the PhET Interactive Simulations team has been working to make science and math more engaging and accessible for all learners, worldwide. The challenge faced by educators is that effective STEM learning environments must support student understanding of core concepts, engage students in STEM practices, and develop students to think like STEM experts. The PhET project has focused on creating simulations that simultaneously address these three learning goals, are grounded in education research, work flexibly with a variety of research-based pedagogies, and promote widespread adoption. Today, our collection of 153 interactive simulations are translated into 93 languages and used over 100 million times per year. In this talk, we will reflect on the journey from 2002 to today, examining critical decision points, lessons learned, and innovations around pedagogy, design, technology, licensing, and dissemination that have influenced PhET’s work and its impact. We will consider the role of education research and the question of what to make (and not make) easily adaptable. Finally, we will look ahead to the challenges and opportunities on the horizon – bringing science inquiry to students with disabilities, advancing teacher practice, growing international use, and building a sustainable business model.