Firms engage increasingly in open business models. While most research has previously focused on typologies or challenges of open business models, their specific antecedents have not been studied so far. We use data from eight open business model cases to explore this question and identify five main antecedents of open business models: (1) business model inconsistency, (2) need to create and capture new value, (3) previous experience with collaboration, (4) open business model patterns, and (5) industry convergence. Based on openness characteristics from the existing literature, we differentiate four basic types of open business models and develop an initial understanding of the relevance of the identified antecedents for each of them. We thereby provide first guidelines for practitioners in choosing the right form of business model openness for their company.