Part I. Theology: 1. 'Adl (rational divine justice); 2.Imamate (legitimate leadership); Part II. Origins: 3. Community; 4. Fragmentation; Part III. Constructing Shi'ism:5. Zaydism in the balance between Sunni and Shi'a; 6. The weight of Isma'ili expectations; 7. Twelver Sh¯i'ism and the problem of the hidden imam; Part IV. Shi'ism in the Modern World: 8. Zaydism at the crossroads; 9. (Nizari Ismi'ilism reconstituted; 10. The politicization of the Twelver Shi'a; Conclusion: Sunni-Shi'i relations.