One professional secret of the legal profession is that often, lawyers don’t necessarily know the law. Not in detail, anyway. Instead of knowing the law, the true skill of lawyers is often knowing how to find the law. The process of finding the law relevant to any legal dilemma which is presented to you, is legal research. The purpose of this chapter is to give you an initial grounding in legal research, and a brief introduction to the most common tools. We will look at legal encyclopaedias (which explain the law systematically, and provide references to statute and cases). We will look at how to find relevant case precedents on a range of databases, some of which are freely available online, and some of which will require a login through your university library. And we will look at how to find statute law (legislation) and the supporting materials which will enable you to understand those statutes. The process of becoming an excellent legal researcher takes time, effort, persistence and patience. It requires systematic thinking and attention to detail. The good news, though, is that anyone with those qualities can learn to do it well.

This chapter explores the existence and nature of international legal norms governing war and peace in the Greek and Roman worlds. Challenging the notion that ancient societies lacked international law due to the absence of sovereign equality, Buis argues that a normative framework did exist, rooted in the projection of domestic legal categories into the interpolity sphere. Through detailed analysis of treaties, declarations of war and conduct during hostilities, the chapter demonstrates how concepts such as justice, self-defence and proportionality were applied to justify and regulate warfare. It also examines the rhetorical and ideological strategies used by hegemonic powers like Athens and Rome to legitimize imperial expansion under the guise of equality and friendship. The chapter concludes that ancient international law was not based on mutual consent among equals but emerged from hegemonic imposition of internal norms, offering valuable insights into the political underpinnings of modern international law.

This chapter explores the evolution and practice of diplomacy in the ancient Near East from the third to the first millennium BC. Drawing on a wide range of textual sources – including letters, treaties and royal inscriptions – it examines how early states and empires developed complex systems of international relations. Key diplomatic mechanisms included the exchange of messengers, gifts and royal women, as well as the swearing of oaths and the negotiation of treaties. The chapter highlights the metaphor of ‘brotherhood’ among kings, the role of divine sanction in alliances and the importance of protocol and etiquette in diplomatic encounters. It also discusses the transition from interpersonal diplomacy among city states to more formalised state-level diplomacy, particularly during the El Amarna period. The chapter concludes by emphasizing the continuity and ritualisation of diplomatic practices over centuries, forming what may be considered the earliest known international system.

This chapter explores the nature and mechanisms of diplomacy in the Greek and Roman worlds, examining how ancient societies managed interstate relations in the absence of modern diplomatic institutions. It argues that while ancient diplomacy lacked formal structures like embassies or foreign ministries, it was nonetheless a sophisticated and essential practice grounded in legal, religious and social norms. The chapter analyses the roles of actors such as ambassadors, heralds and hostages, and the use of instruments like treaties, oaths, gifts and kinship diplomacy. It highlights the fluid boundaries between public and private, law and custom, and emphasises the adaptability of diplomatic practices across time and cultures. Drawing on examples from classical Greece, republican and imperial Rome, and late Antiquity, the chapter shows how diplomacy evolved in response to shifting political realities, and how it reflected broader cultural values and power dynamics. Ultimately, it contends that diplomacy in antiquity was a vital tool for managing conflict, asserting hegemony and fostering co-operation, even if it did not conform to modern definitions.

This chapter explores the legal frameworks and treaty-based mechanisms that governed trade and communication in the Greek and Roman worlds. It examines how international law in antiquity – though lacking modern institutional structures – was shaped through bilateral and multilateral treaties, commercial privileges and legal norms that facilitated cross-border economic exchange. Drawing on epigraphic, literary and legal sources, the chapter analyses trade agreements from Homeric times through the Hellenistic period to the Roman Empire and late Antiquity. Key case studies include Athenian timber monopolies in Macedonia, Roman–Carthaginian treaties regulating commerce and Roman–Persian trade protocols. The chapter also investigates the legal instruments of commercium and enktesis, and the role of isopoliteia treaties in creating shared legal spaces. It argues that while ancient international law was informal and decentralised, it effectively supported economic interconnectivity across diverse polities and empires, laying foundational principles for later legal traditions.

This chapter critically examines the existence and conceptualisation of ‘international law’ in the Greek and Roman world from 600 BC to AD 650. It challenges traditional minimalist views that exclude antiquity from the history of international law and proposes a recalibrated approach grounded in conceptual history. By analysing legal practices, treaties and philosophical notions such as jus gentium and dikaion koinon, the chapter explores how ancient societies regulated interpolity relations. It introduces eight analytical dichotomies – such as inside/outside, city state/empire, and law/non-law – to frame the discussion. Through case studies on war, diplomacy, trade and dispute resolution, the chapter argues that while ancient international law did not exist in a modern sense, it functioned as a prototype for legal norms governing relations between autonomous entities. The chapter concludes that international law in antiquity was not merely a precursor but a meaningful legal system in its own right, shaped by the need to structure a complex and often hostile world.

This chapter explores the existence and nature of international law in the Sasanian Persian Empire, particularly in its relations with Rome and Byzantium. It examines how the Sasanians conceptualized sovereignty, war and diplomacy, and whether they shared legal norms with their Roman counterparts. Drawing on epigraphic, literary and diplomatic sources, the chapter argues that the Sasanians recognized Rome as an equal sovereign power, as reflected in titles, diplomatic language (e.g. ‘brotherhood’), and treaty practices. It also identifies a Sasanian notion akin to the Roman concept of bellum justum, suggesting a shared understanding of just war. The chapter highlights the sophistication of Persian diplomacy, especially in the treaty of AD 561–2, which demonstrates mutual legal procedures, bilingual documentation and protections for religious minorities. These findings support the view that the Sasanian Empire participated in a form of international law, characterised by mutual recognition, legal formalism and evolving norms of coexistence.

This chapter concerns state succession, the process by which a state may succeed to the treaties, assets, debts and responsibilities of a predecessor state. The relationship between continuity and succession of states is not always easy to determine, as some states may be deemed to be continuations of the earlier state in a slightly different form rather than a totally new state. Examples covered here include Russia, Yugoslavia and Germany. The question of succession to treaties is then considered with an examination of the different kinds of treaties, such as multilateral treaties, bilateral treaties, human rights treaties and territorial treaties. The various effects upon such treaties of how the succession is characterised, from absorption and merger to cession of part of a state to another, to the creation of a new state, are examined. The chapter then turns to other branches of succession, from succession to membership of international organisations to succession to assets, including archives, and debts and succession to private rights, nationality and responsibility.

This chapter analyses the concept of jurisdiction, a central feature of territorial sovereignty. The principle of domestic jurisdiction is explained, followed by an examination of the various bases upon which criminal jurisdiction may be exercised by states under international law. The primary basis is the territorial principle, which clearly reflects the key principle of territorial sovereignty. However, jurisdiction may also be exercised on the grounds of nationality, a concept which is domestically defined but which may require international acceptance. Other grounds include the passive personality principle, the protective principle and the universality principle. In terms of the latter, examples may include war crimes and crimes against humanity. In addition, treaties may provide for jurisdiction beyond the accepted principles with regard to drug trafficking and slavery, the taking of hostages and hijacking. The chapter also discusses the effect of the US Alien Tort Statute in the framework of universal jurisdiction. The question of extraterritorial jurisdiction is also noted.

This chapter deals with the question of the sources of international law, that is, how one distinguishes between what is law and what is not. This is governed essentially by art. 38(1) of the Statute of the International Court of Justice. Historically, the first source is custom, which is composed of two elements: the actual conduct of states and the belief that such conduct is carried out in the belief that it is ‘law’. What is counted as state practice is examined, as is the critical belief requirement (opinio juris), which is often harder to ascertain. The process of change is discussed, as is the concept of local or regional custom. The second source, of increasing importance today, is international agreements or treaties, which are binding on all states parties to the particular agreement and is the focus of a later chapter. The third source is termed ‘general principles of law’, which seeks to cover gaps in the law by recourse to accepted principles of the system or of domestic law and includes the notion of equity. Finally, the chapter looks at subsidiary means for the determination of law, including judicial decisions and writings. Other possible sources of law are noted, and the work of the UN International Law Commission is referenced.

The chapter concerns the relationship between international law and domestic or municipal law. Theories of the relationship are referenced. The chapter then turns to the role of domestic or municipal law in international law, with the acceptance of the supremacy in the system of the latter. The chapter focuses, however, upon the role of international law within domestic legal systems with particular emphasis upon the UK. The various shifts in approach are noted with regard to customary international law and the current situation discussed, whereby custom constitutes a source of law and not a part of the common law upon which judges may draw. As far as treaties are concerned, these are not part of UK law unless incorporated. This avoids the situation whereby the executive may legislate merely by becoming a party to a treaty. The situation with regard to the US and other states in both the common law and civil law systems is then reviewed. The chapter ends with an examination of the doctrines of non-justiciability and act of state in various states.

This chapter considers the law of treaties in the light primarily of the key Vienna Convention on the Law of Treaties, 1969, much of which is considered as part of customary law. The chapter discusses the role and nature of international treaties in the light of their binding nature upon states parties (pacta sunt servanda). The making of treaties, from the formalities and methods of consent from signature to ratification, is covered before the chapter turns to reservations. The nature of reservations and their effect upon third parties is addressed is addressed as is the process of amendment of treaties. Consideration of treaty interpretation then follows with the various methodologies examined from the textual, intention and object, and purpose of the treaty points of view, with a careful look at case law. The particular position of human rights treaties in this process is noted. The chapter then turns to the invalidity, termination and suspension of treaties, including a discussion of the concepts of peremptory norms (jus cogens), material breach, supervening impossibility of performance and fundamental change of circumstances (rebus sic stantibus).

This chapter offers a survey of the jus gentium in South East Aasia between the fifteenth and the late eighteenth centuries. It starts by providing an overview of the region and elucidating the challenges inherent in its study. Subsequently, the examination follows three lines of enquiry: first, it explores basic values and principles governing inter-ruler and interpolity relations on the eve of European colonialism around 1450–1500 by discussing and problematising tributary relations. Second, it examines the uniqueness of these relations when juxtaposed with Europe, highlighting key facets such as hierarchy, the prioritisation of people over land, and the forging of alliances with communities of the sea and land. Finally, the chapter plots the transformative impact of European colonial policies and practices, such as the militarisation of maritime spaces, the use of sea passes and the introduction of written agreements and commercial treaties.

Thes chapter argues that both Britons and South Asians made use of instruments such as treaties and a broader world of diplomatic paperwork to construct a framework for interstate legality in the eighteenth century. South Asian efforts to make and remake arrangements with British traders and government agencies constituted a source of inter-imperial legal forms. Inter-imperial treaties were not blunt instruments of European imperialism, but legal documents co-produced by South Asian bureaucrats. By emphasising the activism and political thought of South Asian actors in their pursuit of a new inter-imperial order, this chapter rethinks the focus on European actors as the architects of international law. Of course, multilingual and multipolar claim making did not impose a stable legal order in South Asia. Treaties were regularly abrogated and renegotiated. Nevertheless, such efforts to negotiate relationships among states and enshrine them punctuated and shaped the upheavals of the eighteenth century as well as the explosion of new projects of state building. Inter-imperial lawmaking emerged as a vital site for politics in the eighteenth century.

The international law of the sea treaties imposes various obligations on contracting states, which can be managed more efficiently and cost-effectively through blockchain technology. As a disruptive tool, blockchain allows stakeholders to track transactions in a secure, cryptographically verified public database. It ensures a secure and reliable record of activities and information exchange governed by international agreements. This paper explores how the blockchain-based systems could help protect the maritime community and support sustainable ocean governance under the law of the sea. Particular attention is given to conserving marine living resources, protecting the marine environment and preserving marine biodiversity. Blockchain is already in use for some internationally regulated activities, such as electronic data interchange, though electronic permitting still waits broader international approval. Besides the clear advantages of blockchain, its legal, regulatory and other concerns must be addressed when considering its role in implementing international treaties. The author aims to explore whether harnessing blockchain`s potential requires new international agreement or if a simpler soft law instrument could provide sufficient guidance and safeguards for the international community.

A framing case study examines North Korea’s nuclear tests. Then the chapter examines how states make international law. The chapter specifically discusses: (1) treaties, including entry into treaties, reservations, interpretation, and exit; (2) customary international law, including state practice, acceptance as law (opinio juris), and conceptual challenges; and (3) other important factors, including general principles, unilateral declarations, and peremptory norms (jus cogens).

This chapter examines rights, authority, and autonomy under the Dutch East India Company (VOC) in seventeenth century Southeast Asia. Exploring how the Company managed its employees, Asian treaty partners, and diverse populations under its rule, this chapter is divided into three sections. The first delves into the instruments that granted the Company a range of powers, including the Company charter, commissions, as well as employment and disciplinary contracts. In the 1640s these were later supplemented by the Batavian Statutes. The 2nd section explores the VOC’s interactions with Asian rulers by focusing on treaties and alliances. These treaties curtailed the liberty of Asian rulers, compromised their sovereignty, and reinforced their dependency on the VOC. The 3rd section shifts attention to the VOC’s administration of ethnic and religious communities under its rule.