There is mounting concern that dark commercial patterns may cause substantial consumer detriment. These practices are commonly found in online user interfaces and steer, deceive, coerce, or manipulate consumers into making choices that often are not in their best interests. This report proposes a working definition of dark commercial patterns, sets out evidence of their prevalence, effectiveness and harms, and identifies possible policy and enforcement responses to assist consumer policy makers and authorities in addressing them. It also documents possible approaches that consumers and businesses may take to mitigate dark commercial patterns.