This study will test the momentary, reciprocal dynamics among negative affect and substance use craving, specifically for alcohol and cannabis. Negative reinforcement models of substance use suggest that heightened negative affect are associated with substance use as a means to cope with negative affect. However, a recent EMA meta-analysis suggests that negative affect does not predict alcohol use at the day level (e.g., Dora et al., 2022). A recent line of research (e.g., Waddell, Sher, & Piasecki, 2021; Waddell, Bartholow, & Piasecki, in revision) has suggested that craving/desire to use is a more tractable outcome within such theory, as it is not subject to constraints present for actual substance use (e.g., availability of substances, acceptability of use, time of day). It is also possible that negative affect may only be related to substance use and use-related outcomes in some people. However, previous work has focused on examining group effects. In addition, little is known about whether substance use-related outcomes may impart bidirectional changes in negative affect. Particularly for craving, if one craves substance use but does not use, this may lead to an increase in negative affect, as the individual did not have the experience they were craving. Alternatively, for some people, craving may resolve on its own with minimal impact on affect. Therefore, the current study seeks to separately test the dynamic, reciprocal effects of alcohol and cannabis use craving and negative affect prior to substance use in a sample of community adults who use alcohol and cannabis.