Mainstreaming involves integrating climate adaptation measures into existing policies and programs. This article reviews the policy process and policy capacity of government organizations and suggests that both need to be incorporated into climate change adaptation assessments. A critical part of mainstreaming is evidence-based decision-making, which emphasizes that decision makers should have the best available information in order to make knowledgeable decisions. This requires policy work that involves a wide variety of statistical methods, applied research, and advanced modeling techniques to gauge broad public opinion and attitudes as well as more routine research techniques. A review of previous past quantitative studies conducted mainly in Canada identifies factors driving policy capacity within government departments responsible for formulating, choosing, implementing, and evaluating climate change adaptation policies and programs. Policy capacity has traditionally been objectively measured and includes indicators such as the number of policy staff, their education levels, resources available, roles and tasks, and ongoing training. More attention needs to be paid to the subjective perceptions of individuals who undertake policy work, in particular the attitudes towards the policy-making process. This paper concludes by proposing a policy capacity framework that includes individual, organizational, and sectoral policy capacity considerations.