From the beginning, PhET simulations and resources have worked to embody the results of education research in their design and to prioritize flexibility and teacher agency in how they are used in teaching and learning. That is, baking in the science, while respecting and enabling the art, of teaching. In this talk, I will highlight rich examples of these approaches, and introduce several initiatives at PhET where we are building on these traditions. Our PhET-iO initiative allows customization of sims and provides access to back-end data. Our PhET Global initiative is focusing on teacher leadership and community in Latin America and Africa. And, our newest work will give teachers and learners access to adjustable sources of error and uncertainty in sims.