Despite public health efforts to support smoking cessation, one in five Dutch adults still smokes. People who smoke can make use of digital smoking cessation interventions to support their quit attempt. Such interventions can take the form of a website or an app on a smartphone. Unfortunately, the use of such interventions is suboptimal. This dissertation investigated various ways to optimize digital smoking cessation interventions. Improvement strategies ranged from the technological realization of digital behavior change interventions (e.g., use of animated video instead of text) to questions pertaining to the psychology of smoking cessation (e.g., the role of the smoker’s (social) environment in relapse, information about e-cigarettes). Topical issues were also examined (e.g., the impact of Covid-19 and related regulations on smoking behavior and beliefs about smoking and quitting). A variety of research methods were employed, including experiments and ecological momentary assessments.