We describe the structure of the abstract domains in the Astr�e static analyzer, their modular organization into a hierarchical network, their cooperation to over-approximate the conjunction/reduced product of different abstractions and to ensure termination using collaborative widenings and narrowings. This separation of the abstraction into a combination of cooperative abstract domains makes Astr�e extensible, an essential feature to cope with false alarms and ultimately provide sound formal verification of the absence of runtime errors in very large software.