Learning objectives (LOs) are used to communicate the purpose of instruction. Done well, they convey the expectations that the instructor--and by extension, the academic field--has in terms of what students should know and be able to do after completing a course of study. As a result, they help students better understand course activities and increase student performance on assessments. LOs also serve as the foundation of course design, as they help structure classroom practices and define the focus of assessments. Understanding the research can improve and refine instructor and student use of LOs. This essay describes an online, evidence-based teaching guide published by "CBE--Life Sciences Education" ("LSE") at http://lse.ascb.org/learning-objectives. The guide contains condensed summaries of key research findings organized by recommendations for writing and using LOs, summaries of and links to research articles and other resources, and actionable advice in the form of a checklist for instructors. In addition to describing key features of the guide, we also identify areas that warrant further empirical studies.