Sources of international law describes where binding and non-binding rules of public international law come from in practice, and what lawyers and courts look to when identifying applicable international norms.For the UK and Ireland, the term is usually used descriptively, with reference to Article 38(1) of the Statute of the International Court of Justice, rather than being defined in domestic legislation. It commonly includes: treaties and conventions; customary international law (state practice accepted as law); general principles of law recognised by civilised nations; and, as subsidiary means, international case law and the writings of publicists.In UK courts (including England and Wales, Scotland and Northern Ireland) and Irish courts, sources of international law are relevant when interpreting treaties incorporated into domestic law, developing the common law, applying interpretative presumptions (such as conformity with international obligations), and in advising states and private clients engaged in cross‑border matters.Usage and understanding of the concept are broadly consistent across the four jurisdictions, though the constitutional routes by which international law takes effect domestically differ (for example, dualism in the UK and Ireland and the need for implementing legislation).