So many constraints apply to the use of comparative legal materials in the judicial decision-making process that a recurrent question for academics and judges alike is whether judges should use them at all. Mak's comparative study suggests that research of foreign legal materials takes place in all of the highest courts examined in France, the Netherlands, Canada and in the United States. The only valid question is therefore how foreign law (in the broad sense of binding and non-binding foreign legal sources) can be used in the decision-making of the highest courts. Can judges do more than apparently ‘cherry-picking’ foreign legal materials in their judgments? Mak answers this question in two ways. First, she connects the use of foreign law with systemic factors, such as the model of implementation of international law (eg, monist legal systems or a supranational order such as the European Union), the style of judicial discourse of the highest court, the personal approaches of the highest court judges to the study of foreign law and to judicial discretion in constitutional and legal interpretation. Second, she distinctively relies upon interviews with judicial members of the highest courts in order to introduce a range of judicial approaches to the use of foreign legal materials in the judicial decision-making. These empirical insights have been gained following a rigorous methodology explained in the early chapters of the book and the interviews make this book very readable.

Mak demonstrates that, against an expanding flow of legal sources across borders, judges have to reconsider the ways they search for and weigh arguments in the making of their decisions. Comparative legal research is now institutionalized, through judicial research assistance. Judicial networks make it easier to learn about the treatment of a similar issue in another legal system. Furthermore, judges can direct specific requests to counsel and they receive third-party interveners' submissions including foreign law. Mak is careful not to exaggerate the importance of comparative legal research in judicial decision-making. The need for timely justice, the availability of research assistance to the judge and the general workload of a court all shape and, in practice, limit the possibility of judicial engagement with foreign law. So judges, within the limits of their legal systems, have been adjusting their role and working methods for the deliberation and judgment of cases.

Perhaps Mak's most distinctive contribution is to identify that judges of the highest courts develop judicial leadership through their engagement as ‘partners in a common judicial enterprise’ beyond national boundaries. Judges will cite each other's case law to demonstrate established or emerging patterns informing human rights jurisprudence in the world—subject to shared social practices (eg on abortion). This is legal integration across national borders, with the growth of formally binding foreign legal sources (international treaties, the European Convention on Human Rights and the law of the European Union) and the increase in judicial networks. But Mak goes further and suggests that judges measure themselves with other courts, and that judicial practices in other courts also inform the development of best practices in the judicial decision-making process. Thus, Mak detects the influence of foreign judicial practices in the recent evolution of the domestic style of judgments, with greater elaboration of the arguments in Dutch and French highest courts, and a greater emphasis on majority judgments in Anglo-American courts.

Yet not all comparative legal research within a court produces helpful arguments. Mak rightly points out that foreign legal sources do not offer clear-cut solutions but rather inform the possible interpretation of the domestic law. But why would judges decide to cite non-binding judgments from foreign national jurisdictions or ‘soft law’ instruments, such as the Principles of European Contract Law? References to judicial interviews make Mak's analysis highly pertinent, as she demonstrates how judges look at foreign sources for ideas rather than solutions. When preparing a decision, a judge might use a foreign legal source to help to clarify the domestic arguments. He or she might then cite it when the case is difficult and of public importance, or in order to spot trends regarding the evolution of the law elsewhere, and to determine their own position against these trends.

Mak ultimately demonstrates the importance of the judges' personal approaches to the use of foreign legal sources in the courts' decision-making. Resistance to, or engagement with, foreign law reflects different ideas about the possibility of a convergence between legal regimes. The ‘localist’ judge, in her terms, resists the use of foreign law because the legal culture specific to each legal system is seen as a limiting factor for the harmonization or transplantation of legal solutions. By comparison, the ‘globalist’ judge expects that a convergence of legal regimes in the world can be realized—hence the interest in, and contribution to the development of the law and judicial practices across national legal borders. This is a theme that, inevitably, requires further discussion; it remains a matter of debate whether ‘judicial internationalization’ is, or can be, established to the depth Mak suggests. She concludes, perhaps unduly tentatively, that, contrary to a common assumption, judges do not ‘cherry-pick’ foreign judgments or other non-binding legal materials to support their own decisions. Rather, given the many constraints they are under, judges are not systematic in their use of comparative legal sources in judicial decision-making and so cannot say in precise terms why they consult non-binding foreign sources in one case and not in another case. While the latter question calls for further elaboration, Mak does provide the tools to understand how each national constitutional framework enables or constrains the integration of foreign judicial practices into the accepted definition of the judicial function in that legal system.

Mak's comparative study offers a significant contribution to the scholarship on the use of foreign legal materials in legal developments. The close scrutiny of the inner workings of the highest courts also make it a welcome addition to the field of comparative judicial studies. The book certainly merits attention from both lawyers and political scientists.