This is a novel book. Diplomatic immunity is a form of legal immunity that ensures that diplomats are given safe passage and are considered not susceptible to lawsuit or prosecution under the host country's laws, although they can still be expelled. It was agreed as international law in the Vienna Convention on Diplomatic Relations (1961), though the concept and custom have a much longer history. Many principles of diplomatic immunity are now considered to be customary law. Diplomatic immunity as an institution developed to allow for the maintenance of government relations, including during periods of difficulties and even armed conflict. When receiving diplomats—who formally represent the sovereign—the receiving head of state grants certain privileges and immunities to ensure they may effectively carry out their duties, on the understanding that these are provided on a reciprocal basis. Originally, these privileges and immunities were granted on a bilateral, ad hoc basis, which led to misunderstandings and conflict, pressure on weaker states, and an inability for other states to judge which party was at fault. An international agreement known as the Vienna Conventions codified the rules and agreements, providing standards and privileges to all states.