In Giyoo Hatano's passing, we have lost an esteemed colleague and a treasured friend. Among his many contributions to our field, our work, and our lives, we honor and build on his and his colleagues' work on conceptual growth. We liken the view developed by Hatano and his colleagues to Toulmin's evolutionary scheme for understanding conceptual growth in intellectual disciplines, and we briefly sketch recent studies and discussions in which our methods and conceptualizations depend upon and draw meaning from Hatano's work, findings, and insights. He contributed strongly to the evolutionary growth of conceptual understanding in our scientific field, and he was an important hub of communication and interaction among scientists around the world. We are grateful to have had the chance to interact and learn with Giyoo Hatano, and we will gratefully continue our interaction with his ideas, his contributions, and the relations that he forged across national boundaries.