Warfare was not between individuals but between their sovereigns, and the officers and officials of European governments and armies often changed employers. Truces and ceasefires were commonplace, along with fraternization between officers of enemy armies during them. When prisoners, the officers usually gave their parole and were only restricted to a city away from the theatre of war. Almost always, they were given leave to carry their personal sidearms. Even during French revolutionary wars, British scientists visited the French Academy. In such an atmosphere, it was easy to accept that some persons were immune to the laws. After all, they were still bound by strict requirements of honour and customs.

In the nineteenth century, the Congress of Vienna system reasserted the rights of diplomats, and they have been largely respected since then as the European model has spread throughout the world. Currently, diplomatic immunity, as well as diplomatic relations as a whole, are governed internationally by the Vienna Convention on Diplomatic Relations, which has been ratified by almost every country in the world.

In modern times, diplomatic immunity continues to provide a means, albeit imperfect, to safeguard diplomatic personnel from any animosity that might arise between nations. As one article put it: "So why do we agree to a system in which we're dependent on a foreign country's whim before we can prosecute a criminal inside our own borders? The practical answer is: because we depend on other countries to honor our own diplomats' immunity just as scrupulously as we honor theirs."

Some countries have made reservations to the Vienna Convention on Diplomatic Relations, but they are minor. Most important are the reservation by most Arab nations concerning the immunity of diplomatic bags and non-recognition of Israel. A number of countries limit the diplomatic immunity of persons who are citizens of the receiving country. As nations keep faith to their treaties with differing zeal, other rules may also apply, though in most cases this summary is a reasonably accurate approximation. It is important to note that the Convention does not cover the personnel of international organizations, whose privileges are decided upon on a case-by-case basis, usually in the treaties founding such organizations. The United Nations system (including its agencies, which comprise the most recognizable international bodies such as the World Bank and many others) has a relatively standardized form of limited immunities for staff traveling on U.N. laissez-passer; diplomatic immunity is often granted to the highest-ranking officials of these agencies. Consular officials (that do not have concurrent diplomatic accreditation) formally have a more limited form of immunity, generally limited to their official duties. Diplomatic technical and administrative staff also have more limited immunity under the Vienna Convention; for this reason, some countries may accredit technical and administrative staff as attachés.

Other categories of government officials that may travel frequently to other countries may not have diplomatic passports or diplomatic immunity, such as members of the military, high-ranking government officials, ministers, and others. Many countries provide non-diplomatic official passports to such personnel, and there may be different classes of such travel documents such as official passports, service passports, and others. De facto recognition of some form of immunity may be conveyed by states accepting officials traveling on such documents, or there may exist bilateral agreements to govern such cases (as in, for example, the case of military personnel conducting or observing exercises on the territory of the receiving country).

Formally, diplomatic immunity may be limited to officials accredited to a host country, or traveling to or from their host country. In practice, many countries may effectively recognize diplomatic immunity for those traveling on diplomatic passports, with admittance to the country constituting acceptance of the diplomatic status.

In reality, most diplomats are representatives of nations with a tradition of professional civil service, and are expected to obey regulations governing their behaviour and they suffer strict internal consequences (disciplinary action) if they flout local laws. In many nations a professional diplomat's career may be compromised if he or she (or even members of his or her family) disobeys the local authorities or causes serious embarrassment, and such cases are, at any rate, a violation of the spirit of the Vienna Conventions.

The Vienna Convention is explicit that "without prejudice to their privileges and immunities, it is the duty of all persons enjoying such privileges and immunities to respect the laws and regulations of the receiving State." Nevertheless, in some occasions, diplomatic immunity leads to some unfortunate results; protected diplomats have violated laws (including those that would be violations at home as well) of the host country and that country has been essentially limited to informing the diplomat's nation that the diplomat is no longer welcome (persona non grata). Diplomatic agents are not, however, exempt from the jurisdiction of their home state, and hence prosecution may be undertaken by the sending state; for minor violations of the law, the sending state may impose administrative procedures specific to the foreign service or diplomatic mission.

Violation of the law by diplomats has included espionage, smuggling, child custody law violations, and even murder: in London in 1984, policewoman Yvonne Fletcher was killed on the street by a person shooting from inside the Libyan embassy. The incident caused a breakdown in diplomatic relations until Libya admitted "general responsibility" in 1999.