Numerous methods are available to assess physical activity (PA) but systematic observation (SO) excels in being able to provide contextually rich data on the setting in which the activity occurs. As SO is particularly useful for determining how activity is influenced by the immediate physical and social environments, its use is becoming more popular. Observation tools have the advantages of flexibility, high internal validity, low inference, and low participant burden, while their disadvantages include the need for careful observer training and recalibration, inaccessibility to certain environments, and potential participant reactivity. There is a need for both scientists and practitioners to have additional information on observation techniques and systems relative to making environmental and policy decisions about PA, and in this article, we describe concepts and identify questions related to using SO in researching PA behavior. We present 10 general questions in 3 sections, including those related to: (a) ensuring data accuracy through the selection of the most appropriate methodological protocols; (b) investigating PA in school settings, including physical education, recess, and other programs; and (c) investigating PA in community settings (e.g., parks, recreation centers, youth and adult sport programs) and homes.