Planning effective, engaging lessons and units are challenging tasks for a teacher, but the process can also be meaningful and rewarding. Using a "big understanding"--a guiding statement describing essential content you want students to learn throughout the unit--teachers can successfully plan and create lessons around substantive science content while developing inquiry and literacy skills. In this article, the authors explore a way to both guide your planning and make learning relevant by constructing a big understanding from the unifying concepts of science and your state standards. (Contains 3 figures.)