A theoretical model is presented that examines self-regulatory processes and trainee characteristics as predictors of attrition from voluntary online training in order to determine who is at risk of dropping out and the processes that occur during training that determine when they are at risk of dropping out. Attrition increased following declines in trainees' commitment to training and self-efficacy. Trainees lower in conscientiousness were more vulnerable to dropping out than those higher in conscientiousness, and this effect was fully mediated by self-regulatory processes. Conscientiousness also moderated the effects of commitment and self-efficacy on attrition--a high level of conscientiousness provided a buffer against dropping out when trainees' commitment and self-efficacy declined during training. The number of hours that trainees worked per week moderated the effort/attrition relationship; spending extra time reviewing increased attrition for trainees who worked longer hours and decreased attrition for trainees who worked shorter hours. (Contains 4 figures and 3 tables.)