All courts perform functions of a broadly constitutional kind. They provide a key mechanism for ensuring compliance with law and the peaceful resolution of disputes between people, according to law. Viewed from this perspective, they are integral to the capacity of a state to carry out its responsibility to establish and maintain internal peace and security. 1 In one form or another, courts also are likely to be the forum for the resolution of that most challenging category of legal disputes: enforcing compliance with law by the institutions of the state itself. In each of these respects, courts are central to the rule of law. They may be analysed in terms of separation of powers or representative democracy, as well, where these are features of the constitution of the state.

This chapter is primarily concerned with one category of courts: those with jurisdiction to interpret and apply the Constitution. Because, in some states, multiple courts may have a jurisdiction of this kind, the ambit of the chapter is further confined to apex courts, where final decisions are made. In the world of the twenty- first century, most states have adopted codified constitutions with superior legal status, which are likely to empower one or more courts, expressly or by implication, to evaluate the validity or applicability of legislation by reference to the constitution. Even where a constitution is uncodified, however, as in the United Kingdom and New Zealand, an apex court is likely to apply norms of a constitutional kind and so falls within the scope of the chapter as well.

Most of the 200 or so states or comparable polities of the world have courts with a constitutional jurisdiction. 2 The subject thus offers a rich field for comparison, offering all the familiar opportunities for greater self- understanding, improved knowledge and understanding of others and insights into options for change. The size and diversity of the field, however, also offers equally familiar challenges. 3 To manage these, four cross- cutting schemes of classification, or taxonomies, may be useful. These should not be treated as water- tight compartments, but as aids to the formulation of some initial hypotheses, to be informed or even rebutted by more targeted research for the purposes of more jurisdictionspecifi c projects.

One category distinguishes between states by reference to the degree of adherence to the rule of law, including constitutional law. The distinction maps, very roughly, onto categorizations of states by reference to regime type and to constitutionalism. 4 Hybrid practices on the part of states that occupy an extensive middle ground make bright lines based on any of these criteria notoriously difficult to draw. As a generalization, nevertheless, it is likely to be relevant to consider, in many comparative projects, the extent to which an apex court engages seriously with the task of constitutional review within the limits of its jurisdiction. Unless otherwise specified, courts considered in this chapter broadly comply with this prescription.

A second scheme of classification on which the chapter draws distinguishes between diffuse (or decentralized) and centralized constitutional review. 5 In systems of diffuse review apex courts and, generally, some other courts as well, resolve legal disputes by reference to all sources of law, of which the constitution is one. By contrast, centralized review confers on a Constitutional Court or Tribunal what typically is a monopoly over the interpretation and application of the Constitution, at least in relation to legislation. In various ways, in contemporary conditions of globalization, these two distinct approaches to review are converging. The differences still are sufficiently marked, however, to make the distinction a useful framework for analysis.

Third , in analysing courts with a constitutional jurisdiction it may be relevant to consider the legal system in which review occurs. Granted, this consideration is complicated by the existence of mixed legal systems and the phenomenon of convergence: this time of world legal systems. The prevalent legal system nevertheless may affect both the design of an apex court with constitutional jurisdiction and its operation in practice. Most relevantly, for present purposes, there is a degree of correlation between the legal system and the choice of diffuse or centralized review, insofar as diffuse review tends to be associated with common law legal systems and centralized review with the civil law. While the correlation is by no means invariable, as instances on both sides of the divide show, in each of these cases, the legal system has an impact of a different kind on their operation in practice. 6

Finally , insights into the design and behaviour of apex courts with a constitutional jurisdiction may be derived from the region or subregion in which they are located. Courts of states that are grouped together in a region may exhibit distinctive tendencies stemming from cultures, including histories, that their states share as neighbours. Ideas and practices concerning courts as well as other aspects of government may spread more readily within regions than to other parts of the world. Regional integration affects the apex courts of Member States in ways that are not replicated elsewhere and are necessary for an understanding of the role and functions of courts of this kind. These categories are used as guides to analysis in the rest of the chapter, which is organized as follows. The next two substantive parts describe and explain the two principal prototypes of courts with constitutional jurisdiction by reference to, respectively, diffuse and centralized review. 7 Each of these parts considers the principal characteristics of the form of review with which it is concerned; its spread; and some of the variations to which it is subject. Each also examines two other key aspects of constitutional review: its legitimacy, in terms of the authority for it and the approach to reasoning that is characteristic of this form of review. A brief conclusion draws attention to indicators of future trends.

1 The point applies whether the state is ‘reactive’ or ‘activist’: M.R. Damaska , The Faces of
Justice and State Authority: A Comparative Approach to the Legal Process ( Yale University
Press , 1986 ) 73 , 80 .
2 See the listing compiled by the Venice Commission: Venice Commission, ‘Constitutional
Courts’ ( Council of Europe , 2014), www.venice.coe.int/ webforms/ courts/ (accessed 29
March 2018).
3 C. Saunders , ‘ Towards a Global Constitutional Gene Pool ’ ( 2009 ) 4 ( 3 ) National Taiwan
University Law Review 1 .
4 A.H.Y. Chen , ‘ The Achievement of Constitutionalism in Asia ’, in A.H.Y. Chen (ed.),
Constitutionalism in Asia in the Early Twenty- First Century ( Cambridge University Press,
2014 ) 1 . This and other work by Chen examines earlier schemes of classifi cation by regime
type or constitution to determine their relevance to current conditions, generally and in
particular in Asia.
5 Other terms may be used to describe this distinction: A.H.Y. Chen and M.P. Maduro , ‘ The
Judiciary and Constitutional Review ’, in M. Tushnet , T. Fleiner and C. Saunders (eds.),
Routledge Handbook of Constitutional Law ( Routledge, 2013 ), 97 .
6 The Venice Commission listing shows that the apex courts of around eighteen states depart
from this rule of thumb: Venice Commission (n. 2).