Background: In STEM-innovation implementation processes, PD curriculum materials are designed to support facilitators in conducting professional development. However, little is known about the facilitators' practices in adapting PD materials. This study transfers frameworks from teachers' curriculum adaptation to facilitators and qualitatively investigates adaptation practices of 11 expert facilitators and their underlying individual perspectives in group discussion and interviews. In the study, a framework was developed for capturing facilitators' adaptation practices. Results: The qualitative analysis shows that all so-called materialized adaptation actions (follow, omit, modify, sort, and create) are conducted on different grain sizes of PD material chunks and with various underlying perspectives. Additionally, thematic adaptation actions mainly refer to facilitators' ways of dealing with examples and theoretical constructs. Dealing with examples often involves shifts in forms of knowledge, e.g., when facilitators situate a theoretical construct in concrete classroom practices. The article contributes to theory generation on facilitators' adaptation practices, especially by introducing and illuminating the distinction between materialized and thematic adaptation actions. Conclusion: The empirical insights of various underlying perspectives call for practical consequences for the design of PD curriculum material: To ensure that adaptation practices retain or improve quality, the structure of PD curriculum material must preserve the minimal adequate grain size (better the thematic block than the single slide) and the need for shifts in the forms of addressed knowledge.