Ivan Marcus's groundbreaking work goes right to the heart of issues central to the study of Ashkenaz both currently and in the past, through the fascinating prism of the writing and composition processes of Sefer Ḥasidim. Diving deep into twenty manuscripts and sixty printed editions of the text, Marcus presents Sefer Ḥasidim as an “open book,” by which he means that there is no one single, complete, homogenous work or Ur-text. Marcus writes:

He likens the composition process of Sefer Ḥasidim to an inverted pyramid (4) at whose broad base are thousands of small units of text that the author channeled into a number of parallel versions at the bottom tip (as opposed to numerous variants derived from a single Ur-text at the top of a pyramid). Marcus further determines that all fourteen extant versions of Sefer Ḥasidim are of equal value and that it is not possible to reduce one or the other by sublimating them within any particular hierarchy. That is because “most of the Sefer Hasidim manuscripts contain some paragraph passages that are not found in either SHB [Sefer Ḥasidim Bologna] or SHP [Sefer Ḥasidim Parma], and each edition or small set of editions is independent of SHB and SHP even when one or more blocks of passages appear in more than one of them. The editions differ with respect to the order of the paragraphs as well as the contents” (17). It is this thesis that underlies the book with its accompanying catalog.

The first chapter, following the introduction, lays out the theory of Sefer Ḥasidim as an open book; it presents detailed and convincing evidence for this argument based on the work's entire corpus of manuscripts and printed editions, which attest to the independence of the small textual units within the work's composition processes. Marcus contrasts this open book format to an author's reediting of his own text or to changes made by scribes in the course of the book's transmission. The second chapter examines the “open book” thesis in relation to other texts written by Judah he-Ḥasid and his students, such as Eleazar of Worms, and shows the fluidity and overlapping attached to the concept of text in their writings. A large section of this chapter is devoted to Sefer ha-Ḥasidut, also known as “the French Sefer Ḥasidim,” and examines its structure, historical context, and impact. The chapter ends with a reconsideration of penitential practices in German Pietist writings and in Ashkenaz in general. In the third chapter Marcus presents a biographical profile of Judah he-Ḥasid, compiled by comparing traditions written by his sons and students, hagiographic stories written after his lifetime, and stories from the Sefer Ḥasidim corpus itself. Using a historic-anthropological approach, with all its inherent advantages and disadvantages, Marcus recreates a “tale of four cities” (10)—Speyer, Regensburg, Worms, and Mainz—as a cultural geography related to the biographies of R. Samuel, R. Judah, and R. Eleazar. The chapter concludes with a discussion on what is often a contentious issue for Ashkenaz scholars: whether Hasidei Ashkenaz can best be understood as a movement or as a circle of individuals; and the extent to which depictions of Ashkenazic society in various versions of Sefer Ḥasidim actually have a basis in reality. The fourth chapter sets Sefer Ḥasidim within the broader context of books in Ashkenaz that, according to Marcus, appear to have, “to one degree or another,” an “open book” format, pointing out how the segmented structure and, more limitedly, variations in sequence also appear in other Ashkenazic works across various genres. Marcus concludes that “it is impossible to say that there ever was a single original author's composition” (80) rather than “multiple [and alternative] editions from the beginning” (78), when a Hebrew work is composed of many small textual units that exist in different sequences in more than one manuscript. A worthwhile direction for future study would be for scholars to take up the task of examining the full extent of this phenomenon in Ashkenaz.

Marcus proposes that the norms of the “open book” in Ashkenaz set the limits of an “inward acculturation” (7–9), saying that “in the case of text composition … Jews developed a world of their own, resisting how Latin or vernacular books were composed” (8–9). However, given the fluid and free sense in which he is using the term “open book” in some of his examples in chapter 4, this might perhaps be too broad a generalization (without contradicting Marcus's assumption about continuity between Byzantine Palestine, southern Italy, and Ashkenaz with regards to composition processes of Hebrew books). While it is certainly beyond the scope of Marcus's book to present a comprehensive study of the structure and transmission of Ashkenazic books in manuscripts versus Latin and vernacular books of parallel genres in the high medieval Christian European literature, some comparative examples of this type would have been helpful in strengthening this claim.

The thirty-seven-page catalog of all known manuscripts and printed versions of Sefer Ḥasidim that follows the fourth chapter is a contribution whose importance cannot be overstated. Categorized according to blocks of manuscripts based on various criteria (such as manuscripts that have only one or no known parallel, manuscripts including small clusters of topical paragraphs, manuscripts of Sefer ha-Ḥasidut, etc.), the catalog provides a wealth of information relating to each manuscript that will definitely prove invaluable to scholars in the field. The bibliography itself is an important resource, given its classification of primary material into several subcategories, alongside an extensive bibliography of secondary sources.

By introducing new paradigms of thought, Marcus has changed the state of the art of the field. From now on it will not be possible to study Sefer Ḥasidim on its own or in the broader context of Ashkenaz without relating to all its versions as equal in importance. Marcus's book presents us, on a silver platter, investigative tools of the highest order, the fruit of precise, rigorous, and extensive research into Sefer Ḥasidim. The book moves beyond mere bibliographic references to study culture from a particularly original perspective: the process behind the composition of a Hebrew book in the Middle Ages. Marcus reexamines assumptions previously accepted as absolute truth and his book now stands as a challenge to any future research.