The present study aimed to investigate, from a psychological perspective, the elements that are able to predict attitudes to, and purchases of, organic products. Our specific focus was organic milk due to the reputation established by this product over the years, especially thanks to sales by large retailers. The analysis was performed within the theoretical framework of the Theory of Planned Behavior, which was extended to include trust in supply chain actors and self-identity of the consumers in question as “green consumers”. A large sample of Italian consumers (n = 1509) was interviewed in two stages in order to obtain data regarding both intentions and actual behavior in respect of organic milk purchase. Our results suggest that TPB is, indeed, a predictive model for explaining organic milk purchase intentions and behavior. Furthermore, it can be successfully extended to elements such as self-identity and trust. Yet among all the dimensions of trust in the different actors of the supply chain, only trust in farmers was supported by our results. Therefore, campaigns aimed at fostering trust in farmers could reinforce the position of this food category when required.