Diplomatic law

foreign relations.

economic and cultural relations and administrative cooperation);
It is about peaceful relations;
It is about equal relations (principle of reciprocity);
It is about official relations;
It is about mutual agreement to maintain such relations;
It is about external relations (external nature and between the subjects of international law).

Diplomatic law (DL) – the body of legal rules on the maintenance of peaceful and official relations between subjects of international law through their competent organs.

Int’l law - “the body of rules and principles of action which are binding upon civilized states in their relations with one another (Int’l Law Commission)

Diplomatic relations – the customary form of permanent contact and communication between the subjects of int’l law.

listed in the Statute of the ICJ, Art. 38;
Other sources, not listed in Art. 38 of the Statute of ICJ

of the Statute of the ICJ

“international conventions, whether general or particular, establishing rules expressly recognized by the contesting states” (Statute of ICJ, Art. 38):
Diplomatic normative content;
At least 2 parties;
May codify international custom:
Examples:
Multilateral conventions (such as Vienna Convention on Diplomatic Relations of 1961, Vienna Convention on Consular Relations of 1963, Convention on Special missions of 1969; ..)
Bilateral treaties between States or treaties with IO’s on the questions of DL.

the Statute of the ICJ

 II. international custom, as evidence of a general practice accepted as law (Statute of ICJ, Art. 38):
2 elements: objective (i.e. General practice) and subjective (i.e. Accepted as law, or opinio juris);
General practice = how to identify? -long lasting/widespread/universal character;

of the Statute of the ICJ
III the general principles of law recognized by civilized nations; 
The broad nature of “legal principle”
Nature: generalized national legal principles/general principles of international law;

of the Statute of the ICJ

Subsidiary sources: to fill the gaps or clarify the content of international law norms
judicial decisions and
the teachings of the most highly qualified publicists of the various nations
Note: Decisions of the ICJ binding only for parties, See Art. 59 of the Statute of the ICJ

the Statute of the ICJ

2. The resolutions of international organizations (IOs) if:
2.1. they include the existing norms of diplomatic law; or
2.2. they approve universal international treaties

See the Resolution of General Assembly No 179 (II) on the co-ordination of the privileges and immunities of the United Nations and of specialized agencies

the Statute of ICJ

3. Procedural rules of international conferences (just some of them have the status of customary rule);
4. Unilateral acts in the context of some specific factual or legal situations may create legal obligations:
4.1. statements of the head of the state (See ICJ judgment (1974) in the Nuclear Test case)
4.2. protests (to indicate the state’s negative reaction to the actions of another state or to stress the illegitimate nature of these actions): (e.g. http://urm.lt/default/en/news/lithuanian-foreign-ministry-sends-a-note-of-protest-to-russian-embassy-over-illegal-actions-in-detaining-lithuanias-fishing-vessel-)

the Statute of ICJ

In the widest sense (because they cannot create, change or repeal DL norms, just serve for the purpose of implementation or interpretation) also:
National laws (usually on the status of the state’s or IO’s missions or the functioning of the diplomatic service)
The doctrine of diplomatic law;

bodies are competent to represent the state and how)
State’s institutions for foreign relations: permanent (e.g. diplomatic missions, consular post, etc.) and temporary (e.g. special missions)
The Head of the State;
Parliament;
Government;
Ministry for Foreign Relations.
Other ministries.

the power to represent the State ex officio, so the actions of the Head of the State are equal to the actions of the State;
Usually accepts the credentials, appoints the representatives, negotiates with the heads and other officials of other States, concludes the treaties (the concrete powers of the Head of the State depend on the political regime)

questions, ratifies the int’l treaties, assigns the budget, pass the memoranda or resolutions...
Usually have permanent commissions for foreign relations; send delegations, develop inter-parliamentary diplomacy..