This engaging book begins with Deborah Hertz's story of her discovery thirty years ago of detailed records of Jewish conversions in Berlin going back centuries. For the aspiring young social historian, the find must have seemed providential, at the high tide of quantitative methods that placed a premium on massive data. It was the perfect source for the reconstruction of the history of Jewish conversion, at least from the perspective of a social history that emphasized bare numbers. That the records had been amassed from far-flung church records across the city by a Nazi bureaucracy interested in racial classification was poignant, but could not detract from the immense value of the records in reconstructing the chronology and rate of Jewish conversion.

Hertz's first chapter is a reflection on the tainted origins of these nevertheless precious sources. At the same time that Hertz's book appeared, Eric Ehrenreich published a book-length study of Nazi genealogical science, The Nazi Ancestral Proof: Genealogy, Racial Science, and the Final Solution (Bloomington, IN: Indiana University Press, 2007). While Ehrenreich's study of the genealogy bureaucracy in the context of Nazi racial science is itself a rich achievement, Hertz succeeds in a few opening pages of this well-written study in evoking some further fascinating details, including the office's cooperation with the Jewish community's own genealogical authority, and its complicated leader, Jacob Jacobson.

What to do with the data? Since the 1970s, after all, the historical profession has moved on from the heroic era of quantitative social history, of which Hertz's charts of aggregated information—relegated to an appendix—are an obvious vestige. Given her chapter-length focus on the records, one of the surprises of How Jews Became German is how little the social historical data figure in the reconstruction of conversion history that follows. They enter at a few moments, but Hertz not only supplements but almost displaces analysis of the numbers with investigation of famous and unknown cases of personal choice to cross the line to Christianity, intersecting the themes of German discrimination, social advancement, and “Jewish self-hatred” as she does so. These “cameo dramas” are the real heart of the book, and undoubtedly succeed in illustrating a great deal (p. 222).

In the early period of Jewish migration to Berlin in the century after 1671, Hertz emphasizes the more strictly religious or even theological basis of conversion, in an atmosphere of Protestant missionary zeal and Christian Hebraism (also carefully analyzed by Christopher Clark fifteen years ago). Hertz then crosses the terrain of Hannah Arendt—and Hertz's own prior work on Jewish salonnières—in spending most of her time with Rahel Levin Varnhagen, her family, and friends, as they struggle with the decision to convert. Hertz's longest chapter, however, is devoted to the two years straddling the Prussian Edict of Emancipation in 1812, in an atmosphere of liberatory warfare and the burgeoning nationalism of Father Friedrich Ludwig Jahn and others. Hertz's book concludes with chapters taking the story through the 1830s, in part to explain the decline in the rate of conversion per capita that would continue, by and large, through the century. One answer, seemingly, is the creation of a Reform Judaism that offered less decisive a choice between the cultural trappings of Judaism and those of German modernity. When the services held in the home of the wealthy Beer family were shut down in the 1820s, the data show that conversions rose correspondingly. In what is the most analytically rich passage of the book, giving up life stories to examine contending explanations of what the data show, Hertz considers this correlation likely a causal relationship, along with a number of other factors (pp. 191–97).

To what is nevertheless overwhelmingly a narrative of personal lives and individual choices, there are really only two queries to be made. As noted, one way to read this book is about the sequel to find a data-driven social history: how exactly to complement its quantitative basis with qualitative investigation. Here it is not clear that one could offer Hertz's book as a general model, in spite of its success on its own terms. For on the one hand, one has the aggregate data, and the other, vividly presented individual lives, with only an intermittent and occasional drive to connect them. To put it differently, Hertz sees the need for something more than the numbers, and her general response is anecdote. The question then is what approach drives the interpretation of personal choices to convert or not. In opening and closing especially, Hertz adopts a disarming first-person voice. “I have written this book because I cannot decide whether a passionate ethnic identity is necessary for personal happiness,” she begins. “[A]s research progressed,” she confesses in the end, “I sometimes lost my sympathy and became disappointed with episodes of apparent hypocrisy, self-hatred, and crass self-promotion.” “You, my readers, can continue to unravel the puzzles and paradoxes of Jewish assimilation,” she writes on the last page (pp. ix, 217, 222). One shares Hertz's judgments all along, but the usually impressionistic register of analysis leaves one confused about why. There is no doubt, however, that Hertz has beautifully individualized the psychology of conversion throughout.

This question about the analytical value of anecdote leads to a second. Hertz is interested not simply in formal conversion, but in “assimilation.” Yet it is not obvious how these two categories are related, and in fact Hertz's move to anecdote, without any overall theoretical approach to cultural identity, leaves their connection something of a mystery. Hertz doesn't register here the severe stress that historians of Jewish culture as different as Scott Spector and Michael Stanislawski have recently placed on the very category of “assimilation,” and on my reading there is no new approach here to the problem of studying cultural identity that would offer an implicit response to the difficulties of that category. Weren't Jews already German before they converted? Even once they did, were they not Jewish still? If the study of identity cannot operate with the formally neat distinction between Jew and Christian that conversion provides, then the latter is obviously no proxy for the former. To come to grips with either, in any event, one would need not simply the human response to difficult quandaries this accomplished and memorable study ends up mainly providing, but some complex account of personal identity in shifting cultural moments.