Policy is not made in a vacuum. Disputes over tobacco control are fought within changing policy environments. This chapter explores key population-level factors that influence a national government's decision to adopt tobacco control policy measures. These factors include social norms about smoking, the proportion of smokers in the population, societal support for tobacco control, and cultural values. These factors are interrelated in a specific way and to understand this, we will take a short detour into what is sometimes called "system thinking in tobacco control." Ten years ago, the US National Cancer Institute (NCI) published a monograph on this topic (Best, Clark, Leichow, & Trochim, 2007), which acknowledged the complexity of tobacco control at the national level, involving as it does the interplay of factors over long periods of time, including feedback loops. According to experts from the NCI, a government's willingness to acknowledge and address the smoking problem follows from its level of awareness that tobacco is a problem, and from the balance of lobbying forces that propose or hold back policy solutions. A government's awareness of the problems associated with tobacco is further affected by specific population factors that are amenable to change. A country's smoking rate is one of these: as long as the proportion of smokers is high, the government is more likely to be aware that there is a public health risk that needs to be addressed. Changes in the number of smokers also affect public support for tobacco control, which increases when adult smoking rates go