In Concubines in Court, Lisa Tran argues that although legal historians have not studied the legal concept of monogamy as widely as equality, monogamy was just as important to remaking Chinese society during the Republican and Communist eras. Tran builds on Qing-era legal histories on chastity, which explain how the neo-Confucian female virtue of chastity shaped a woman's legal relationship to her spouse and to the state, to explore how the twentieth-century moral and legal concept of monogamy forged a new relationship between state and society. According to Tran, monogamy drew on the same late imperial concept of one husband, one wife (yifu yiqi) as chastity, but monogamy also incorporated so-called “universal” political and legal doctrines, which aimed to make China's legal system appear modern to European, American, and Japanese observers. Thus, whereas the late imperial concept of yifu yiqi, as understood through chastity, required only that a wife be loyal to one husband, monogamy extended the meaning to refer to husbands as well as wives. Thus, monogamy aimed not only to transform marriage relationships and to remake the family structure, but also to bring about gender equality.

Drawing on extensive archival sources on legal debates, legislative reforms, and actual court cases, Tran outlines how the concept of monogamy was integrated into China's legal framework, and illuminates more generally how legal reform redefined the relationship between state and society during the first half of the twentieth century. Moreover, in crossing the 1949 divide, Tran aims to introduce a more holistic understanding of legal and social change in twentieth-century China, revising historical conventions that suggest that the Republican era was chaotic and that Communists were authoritarian and inflexible.

Tran describes the Republican era as a transitional period of productive legal change. Because the Republican Civil Code was not implemented until 1929 and 1930, jurists were forced to implement the new concept of monogamy under the Qing civil code. While the drafters of the Guomindang Civil Code may have been committed to monogamy as a legal concept, they tolerated concubinage in practice. Indeed, Tran reminds us that even Chiang Kai-shek (Jiang Jieshi) and Wang Chonghui, an eminent jurist who advised the drafting of the Civil Code, both had concubines. Thus, rather than outlaw concubinage, Republican-era lawmakers simply erased “concubine” as a legal marital category. The Communists, by contrast, recognized concubines as legal wives equal to first wives, and while they mostly tolerated existing cases of concubinage that were not brought before the court, they explicitly outlawed the practice moving forward. Thus, Tran argues that the state's understanding of the relationship between a concubine and a man changed from minor wife in late imperial China, to adultery in the Republican era, and finally to bigamy under Communism.

While historical changes in the law may have followed this clear historical trajectory, individual court cases suggest that concubinage as a social practice was far more complex. Tran's descriptions of legal cases involving concubines reveal that the incorporation of monogamy into the law did not always match the social realities of everyday life. Moreover, these legal conflicts help to elucidate an understudied social history of concubines. Tran critiques earlier revisionist feminist histories of late imperial China for focusing on the agency of main wives and not concubines, but in many ways the transitory nature of the law in twentieth-century China makes this history visible for the first time. The erasure of concubines from the Guomindang Civil Code became an opportunity for concubines to tell their stories through police and court records. On the one hand, concubines engaged with the court through the mediation of jurists' stereotypes, often appearing either as pitiable innocents or as vixens out to get money. But concubines also exerted individual agency, especially as they became central to legal debates over how a modern marriage and family were to be defined. In cases where they demanded support from a deceased male partner's family, concubines pushed the definition of family to include cohabitation rather than kinship. When the wedding ceremony became the new legal criterion for marriage, concubines who tried to claim status as married challenged jurists' understandings of what a modern wedding ceremony should look like.

This groundbreaking legal history of concubinage opens the door to further studies on the social and cultural history of concubines in twentieth-century China. Court cases suggest that there were multiple types of concubines in twentieth-century China. Concubines played a reproductive role in households where they were taken in to continue the patriline, or they could be viewed as a commodity signifying a man's power and social status. Some concubines also may have been former prostitutes, and thus symbols of sexual pleasure. Thus, far from static remnants of a feudal society, concubines during the twentieth century reinvented their social and cultural roles to suit a period of transition.