In more than a century of geniza scholarship, certain themes have continually taken center stage in our progressive understanding of medieval Mediterranean society. The nature of the Jewish community counts among those themes, if nothing else, because the Genizah's documents frequently discuss communal offices and workings, without necessarily explicating them. In Heresy and the Politics of Community, Marina Rustow addresses this topic through the lens of Karaite-Rabbanite relations. Rustow propounds not only the integration of the Karaites and Rabbanites but also the Karaites' conspicuous—sometimes decisive—power in shaping the Jewish politics of the Fatimid Empire. With engaging prose, vigorous argumentation, and topical focus, Rustow succeeds in taking the conversation to the next level, if not a radically new direction.

Heresy and the Politics of Community falls into four parts that illustrate Karaite–Rabbanite complicity and even intimacy. In Part 1, Rustow describes the westward migration of both Iraqi Rabbanites and eastern Karaites, from Mesopotamia to Palestine and Egypt, the traditional stronghold of the Rabbanites of the Palestinian school. She highlights their shared biblical commitments and the diffuse nature of their power, which encouraged dynamic coalition building. Part 2 applies this theory to, among others, the Cairene Rabbanite leader Elḥanan b. Shemarya, who attempted to secede from the Jerusalem and Iraqi academies. His move made surprisingly easy bedfellows of the Rabbanites and Karaites, since the latter, according to Rustow, were ready “to use their political power in the service of the ga'on of Jerusalem, including stamping out the embers of a Rabbanite rebellion in Fustat if needed” (164). Part 3 builds on the works of Judith Olszowy-Schlanger and others, in discussing Rabbanite-Karaite marriage, as well as other points of intersection and overlap in family and civil law. This part establishes the underlying terms by which Karaites and Rabbanites interacted, and as such, it might have been better placed directly after (or in) Part 1, for the sake of leaving the chronologically ordered argument of Parts 2 and 4 in direct sequence. Part 4 addresses the particular causes célèbres of the mid-to-late eleventh century, most notably the sagas of Shelomo b. Yehuda and Daniel b. ‘Azarya. Alliances breached sectarian lines and forged, in 1080, in the office of the Head of the Jews (ra’īs al-yahūd), the oft-disputed presidency of Fatimid Jewry, Karaite and Rabbanite alike. At the risk of overemphasizing the role of the Karaites, such as the eminently well-connected Tustarī clan, Rustow brings significant coherence to the story of the Fatimid Jewry by foregrounding the Karaites' role as a lynchpin in political developments.

Rustow concludes with an epilogue that updates the historical narrative of Jewish heresy and orthodoxy. Here, she iterates the now-standard understanding of the historical and political contingency of the appellations heresy and orthodoxy. Merely attempts at prescription rather than dispassionate description, these categories mask a scrappier reality: Karaites and Rabbanites in the Fatimid Empire (in contrast to Spain) simultaneously jockeyed and collaborated with one another, without partisan scruple, in ways that both presumed full participation and conspired to shape the community. Finally, Rustow's very helpful back matter includes a glossary and guide to people and places.

Placing herself squarely in the dominant school of Genizah scholarship, Rustow treats Karaite-Rabbanite mutual recognition (what Zvi Ankori calls their “fraternity of fate”) as axiomatic, even as she follows the historiographically enshrined communal-doctrinal boundaries that distinguished them. Rustow's innovation lies in her flattening of the political landscape and its presumed hierarchy, according to which the Rabbanites were thought to have related amongst themselves at a higher, more empowered plane, thence treating the Karaites at one level removed.

Rustow's reconstruction also disrupts assumptions about sectarianism as a concept (she avoids “sect” in favor of madhhab, or “school of thought”). She both points out cases of cross-sectarian collusion that bridged supposed fault lines, and also demonstrates fissures within given schools. For example, in Chapter 2 Rustow points out that the calendar's indeterminacy did not follow communal lines between Karaites and Rabbanites, but reflected a much messier picture within the ranks of both, as the well-known Palestinian-Iraqi calendar dispute between Ben-Me'ir and Se‘adya Gaon starkly illustrates.

Though revisiting Jewish partisanship, Heresy and the Politics of Community does not give in to the temptation to erase sectarian boundaries altogether. Rustow points out, on the one hand, the instability of “overlapping strata of religious and communal organization,” which ostensibly promoted partisanship among adherents of the various schools:

On the other hand, her entire book takes for granted and relies on the core stability of those categories. Though a Karaite might donate to Rabbanite yeshiva, one's affiliation—though not immutable—continued to mean something.

The violation of categories might lead to one of two conclusions: Either the categories mean less than they claim to; or the sources’ attention to generic violations betrays their exceptionality, presupposing and thereby reaffirming the vigor of sectarian boundaries. Rustow successfully walks a fine line between the two options. To wit: Karaite–Rabbanite marriages reveal the porosity of partisanship. But insofar as the marriage contracts stipulate specific terms for the preservation of the couple's divergent ritual commitments, they also instantiate those core differences. The Karaite Ben Sha‘yā's marriage contract stipulates no religious protections for his own practice, whereas the Rabbanite Yaḥyā agreed not to “profane against his [Karaite] wife the festivals of the Lord according to the sighting of the moon” (249). Ultimately, Rustow argues that geographic lines of solidarity superseded sectarian ones among Karaites and Rabbanites. However, geography superseded madhhab, not in the sense of negating sectarianism but rather in the sense of subsuming it as a secondary political priority.

Perhaps more difficult is Rustow's illustration of the nature of power itself, not only among Jews but in general, too. In Chapter 3, Rustow brings the notion of patronage to bear, as an individual relationship binding two parties but failing to define bureaucratic or functional roles. Patronage helps to explain both the nonpyramidal nature of Jewish power and the flexibility of its negotiation, both internally and externally. In this regard, she falls close to the middle ground of Mark Cohen's typology of Jewish historiography, and owes much to it.

But Rustow glosses over at least one salient factor in describing Jewish autonomy: taxation. She justifiably challenges the twentieth-century characterization of the medieval Jewish community as a state-within-a-state. However, in arguing a diffusion of power among various constituencies and individuals, she claims that “there was no evidence of a link between the caliphs and Jewish self-government beyond the exilarch's power to collect the dhimmī head-tax (jizya) from the Jews” (71). With barely a nod to the power of the purse, Rustow dismisses what is in fact a serious point of historical interpretation. The ability to collect taxes sits at the fulcrum of both symbolic and practical power: Looking upward, dhimmi representatives funneled resources to the state, bearing the weight of communal responsibility; while looking downward toward their minority constituency, the tax-aggregators sat atop an economic pyramid (or pyramids) built on assessment and distribution of wealth.

One of Rustow's great merits is her ability to render the jumble of contracts and communiqués into a coherent narrative. More than her venerable predecessors, many of whom pioneered this research, Rustow not only collates the sources but also artfully weaves them into stories, replete with intrigue and drama. The eleventh-century power plays, namely, the Geonic schism of 1038–1042 (between Shelomo b. Yehuda and Natan b. Avraham) and the later machinations of Daniel b. ‘Azarya and his son, David b. Daniel, come alive on the page.

Rustow's primary conceit, namely, the productive tension of internal partisan politics, will serve as an important frame through which to analyze the Jewish communities of the Eastern Mediterranean.