This chapter identifies a series of challenging questions and issues that arise frequently during professional development related to the Next Generation Science Standards (NGSS). Through discussions, reflections, and workshop evaluations, we identified a number of issues—sticking points—that tended to generate anxiety and bog down discussions. For many of these questions, answers simply are not known. In these cases, you should avoid the urge to speculate and start a “parking lot” for issues that you can follow up on later. Teacher background information, standards, and references are provided. This book selection also includes the Table of Contents, About the Authors, Contributors, A Letter from David L. Evans, Introduction, and Index.