Patient nonattendance to scheduled sessions results in excessive costs to mental health and substance abuse providers and compromises the care of clients. This paper presents a comprehensive review of interventions that have been shown to increase session attendance rates in these settings. Unique to other review papers, reliability estimates were performed in the selection and evaluation of obtained studies. Reliability of article selection and evaluation strategies was excellent (.80 to .88). Study results indicate several attendance improvement methods appear to be particularly promising, such as scheduling appointments promptly, reminder letters and telephone calls, soliciting patient commitment, and helping to resolve obstacles to attending the session. The specific manner in which these interventions are implemented appears to influence session attendance rates. Moreover, some attendance improvement interventions are clearly effective in some settings, but not others. Specific recommendations are provided in light of the study findings.