The National Science Teaching Association (NSTA) and the "Next Generation Science Standards" ("NGSS") have attempted to make planning easier for teachers by creating a common resource bank, but there is no unit design process specifically created for science teachers in a project- and inquiry-based classroom. Without a common set of guiding principles of unit design, the ability for science teachers to create "NGSS"-aligned units on their own is a very daunting endeavor. This article provides a brief synopsis of the guiding principles of unit development, the planning guide that was created using these principles, and how the principles and planning guide supported the development of a new inquiry-driven unit.