A systematic review of 22 studies (1993–2009) examined the role of self-monitoring in weight loss interventions, focusing on diet, exercise, and self-weighing. Self-monitoring, including diet records, exercise logs, and weight tracking, was consistently linked to weight loss, though evidence was limited due to methodological issues. Most studies used paper diaries, with technology like electronic scales and PDAs used in some. Descriptive designs were common in earlier studies, while more recent ones used randomized trials. Self-monitoring adherence was measured by diary completion or frequency of log-ins. Studies showed that more frequent self-monitoring was associated with greater weight loss, but the optimal frequency was unclear. Self-weighing, especially daily, was linked to better weight loss outcomes. However, most studies had homogeneous samples, predominantly White and female, limiting generalizability. The review highlights the need for more diverse populations, objective measures of adherence, and research on the required dose of self-monitoring for effective weight loss. Technology may improve adherence by making self-monitoring easier. Despite methodological limitations, the evidence supports self-monitoring as a key component of successful weight management. Future research should focus on underrepresented groups and validate self-reported data with objective measures.A systematic review of 22 studies (1993–2009) examined the role of self-monitoring in weight loss interventions, focusing on diet, exercise, and self-weighing. Self-monitoring, including diet records, exercise logs, and weight tracking, was consistently linked to weight loss, though evidence was limited due to methodological issues. Most studies used paper diaries, with technology like electronic scales and PDAs used in some. Descriptive designs were common in earlier studies, while more recent ones used randomized trials. Self-monitoring adherence was measured by diary completion or frequency of log-ins. Studies showed that more frequent self-monitoring was associated with greater weight loss, but the optimal frequency was unclear. Self-weighing, especially daily, was linked to better weight loss outcomes. However, most studies had homogeneous samples, predominantly White and female, limiting generalizability. The review highlights the need for more diverse populations, objective measures of adherence, and research on the required dose of self-monitoring for effective weight loss. Technology may improve adherence by making self-monitoring easier. Despite methodological limitations, the evidence supports self-monitoring as a key component of successful weight management. Future research should focus on underrepresented groups and validate self-reported data with objective measures.