Representing Their Country's Head of State

• Ambassadors serve as direct representatives of their countries' heads of state. By extension, they also represent their country, and are expected to make a good impression --- meeting with other ambassadors, hosting and attending social gatherings and learning as much as possible about the customs and traditions of the country in which the diplomatic mission is located. Because diplomacy is highly bound up in tradition and formality, ambassadors must be conversant in those rules, written and unwritten, as well.
  
  

Advancing Their Country's Interests

• Ambassadors are also meant to directly advance the goals of their respective countries. For example, if the United States is involved in a trade negotiation or attempting to settle a legal dispute, the ambassador's role is to ensure that the position of the United States' government is clearly understood. They are also empowered to carry out negotiations with other ambassadors in order to accomplish those goals --- for example, by working with global entities like the United Nations or the World Trade Organization.
  
  

Report to Their Government

• Ambassadors don't operate in a vacuum; they must report back to their governments with information about the countries in which they're deployed. For example, if a country becomes subject to economic difficulties or civil unrest, it's the responsibility of that country's American ambassador to be a primary source of information for the United States Government, allowing them to evaluate the situation and, if necessary, take action to protect their citizens abroad.
  
  

Coordinate the Diplomatic Mission

• Ambassadors are high-ranking individuals with sweeping authority that they use to organize a country's operations abroad. Frequently, the relations between two countries are too complex for one person to handle, and a diplomatic post consists of many individuals with specialized tasks in addition to the other government agencies operating offices within that country. In such situations, the ambassador is expected to coordinate all operations, so that different agencies and people with different tasks nonetheless work seamlessly together.