The Vienna Convention on Diplomatic Relations states:

“The functions of a diplomatic mission consist, inter alia, in representing the sending State in the receiving State; protecting in the receiving State the interests of the sending State and of its nationals, within the limits permitted by international law; negotiating with the Government of the receiving State; ascertaining by all lawful means conditions and developments in the receiving State, and reporting thereon to the Government of the sending State; promoting friendly relations between the sending State and the receiving State, and developing their economic, cultural and scientific relations.”

 

See the Heads of the Missions abroad here.