Acquiring knowledge about science is an important part of developing scientific expertise. However, students can know many facts about science and yet fail to achieve highly on certain kinds of assessments, or to feel that the subject is personally meaningful. The concept of scientific understanding is examined to explain the gap that exists between knowing about science and successful learning. Models of scientific understanding suggest a number of strategies to support science learning that go beyond acquiring knowledge. It is argued that acquiring scientific knowledge is the first step in an extended process of developing understanding.