In this chapter, the AGM model as applied specifically to belief bases is discussed, contrasting this approach with the belief sets models. Structural intricacies and distinct features of belief bases are outlined, along with revised postulates tailored to base change operations. The chapter presents constructive models, including partial meet and kernel base change operators, generalized partial meet and kernel contractions, basic AGM-generated base contractions and revisions and ensconcement-based contractions.