Anxiety disorders are among the most common classes of mental disorders and come with heavy personal and societal burdens. The current gold standard for the treatment of anxiety disorders is cognitive behavioral therapy (CBT). Although effective, a significant proportion of people with anxiety disorders do not sufficiently benefit from treatment, making it important for researchers to seek ways to maximize treatment effectiveness. Mindfulness-based interventions represent a promising treatment approach for anxiety symptoms. This chapter provides an overview of theories of anxiety and how mindfulness can be beneficial in its treatment. Research on the mechanisms of mindfulness in the reduction of anxiety symptoms is reviewed, and a case is made for its potential effect on intolerance of uncertainty. The chapter concludes with a summary and brief discussion of future research avenues.