Introduction; – Representing Doxastic States : Prioritized Belief Bases, Entrenchment, Systems of Spheres; – Variants of Expansion; – Radical revision; – Conservative Revision; – Moderate Revision; – Restrained Revision; –Variants of Contraction; – Refinement : Neither Revision nor Contraction; – Two-Dimensional Operators : Revision by Comparison; – Two-Dimensional Operators : Cantwell’s Lowering; – Gentle Raising and Lowering; – Two-Dimensional Operators : Raising and Lowering by Strict Comparisons; – Two-Dimensional Operators : Bounded Revision; – Conclusion.