Although preschool principals are important for integrating sustainability,studies on this topic are scarce. Using an embedded mixed methodsapproach, this study explored and compared 50 principals’ views andactions relating to sustainability in the operations of 25 eco- and 25non-eco-certified randomly sampled preschools from 25 municipalities(of a total 290) in Sweden. Using a semi-structured questionnaire, datawas collected from the principals of the preschools. Whole SchoolApproach Flower Model was used as an analytical framework to analyzequalitative data, while quantitative data was subject to OrthogonalProjections to Latent Structures Discriminatory Analysis. According to theparticipating principals, eco-certified preschools focused on increasingchildren’s knowledge about and interests in sustainability, whereasnon-eco-certified preschools focused on strategies to develop teachers’sustainability competence. This is consistent with findings that principalsat eco-certified preschools have a more nuanced and multifaceted viewof sustainability in their leadership practice, indicating thateco-certification, to some extent, plays an important role in making adifference. The study also highlights the potential of adopting a wholeschool approach to sustainability within preschool education.Cross-validation supported the generalizability of the conclusions, at leastwithin a Swedish context.