PUBLIC INTERNATIONA L LAW2
applies where national legal system s leave off: while the latter govern
relations of persons within states, international law essentially governs
relations between states themselves. Moreover, unlike the multiplicity
of national legal systems that exist worldwide, there is one universally
applicable international legal system regulating the entire international
International law yers and judges use a var iety of terms to de scribe
national law, the most common of which are “domestic,” “internal,”
or “municipal” law. A ll of these are me ant to emphasize its distinct
character when juxtaposed with international law. As a concrete ex-
ample, the entire Canadia n legal system (including the Canadian Con-
stitution; all federal, provincial, a nd mun icipal laws and regulations;
the common law; a nd a ll Canadian legal structures and institutions)
would be described by international lawyers as a n ational (or “domes-
tic,” “internal,” or “municipal”) legal system. So too would the Russian
or Costa Rican legal systems, for example. In contrast, t he law govern-
ing Canada’s relationship with Russia or Costa Rica or any other state
would be described as inter national law.
As we shall see further below, the substantive scope of internation-
al law has grown since the mid-twentieth century to include many sub-
ject-areas that traditionally were considered to be of concern only to
domestic legal systems.6 Along with this subst antive expansion have
come new players in the international legal system, some — for instance,
the United Nations a nd other i nternational organizations — with for-
mal capacities within that system, and others — such as indiv iduals
and non-governmental organizations — with more limited or informal
roles.7 As a result, it is no longer accurate to think of international
law solely in terms of the mutual legal rights and obligations of states.
Rather, it now includes rules and mecha nisms governing the relat ions
of states, international organizations and, i n a limited number of area s
of concern to t he international community generally, individuals and
in many ways (see, for ex ample, Chapter 3, Section C(4), as well a s Chapters 6,
8, and 9) but are nevertheles s generally considered to be di stinct systems.
5 Although it should be noted t hat within that sy stem are a number of regional
sub-system s focused on particul ar areas of internation al law of particular i nter-
est to certa in groupings of states: see, for ex ample, Chapter 5, Section D and
Chapter 10, Section C. Such reg ional sub-systems ar e built, however, on the
common substrat um of the universally applic able international legal s ystem.
6 The most prominent exa mple of this is probably the advent of inte rnational hu-
man right s law: see Chapter 10.
7 We explore the intern ational legal personal ity of various players in th e inter-
national lega l system below in Chapter 2.