Trust is considered an important factor for successful collective action in groups of small-holder farmers. A prime example is collective commercialization of agricultural produce through producer organizations. While previous research has focused on trust as an exogenous determinant of participation in groups, this article tests whether trust within exist- ing groups can be improved using a training program. We conduct a cluster-randomized controlled trial in rural Senegal to identify the effects of training members and/or leaders with respect to commercialization on intragroup trust. Our design allows identifying both direct treatment effects of having participated in the training and spillover effects on farmers who did not partake. Looking at different measures of trust in leaders’ competence and motives and of trust in members, we find that participating in the training significantly enhances both trust in leaders and trust in members. For trust in leaders, we also find a strong spillover effect. Our findings suggest that relatively soft and noncostly interventions such as group training appear to positively affect trust within producer organizations.