When people interact with digital technologies, their choices are often driven in a specific direction, mainly through user interface designs—e.g., specific layout or content. Such guiding practices might be useful. They may help find desired information quicker or proceed with a given task more efficiently. Ultimately, they may contribute to improved usability and satisfaction that users experience during the interaction. However, some of such designs can mislead, manipulate, or trick users into choices that are beneficial to service providers but not necessarily to users. These designs are known as dark patterns, and their success relies on psychological characteristics, particularly exploiting decision-making processes’ weaknesses. The applicability of dark patterns is traditionally associated with e-commerce or marketing strategies aiming to increase sales. However, research shows that dark patterns also extend to online privacy, resulting in harms reaching beyond economic loss and exploiting the vulnerabilities of individuals. This chapter reviews research on dark patterns and explains some of the psychological bases that dark patterns rely on. The chapter focuses on privacy issues and discusses possible ways of preventing the detrimental effects of dark patterns, including their effects on business.