I’ll start with something very bureaucratic to explain what public diplomacy is - USIA’s mission statement, which defines public diplomacy as well as anything I’ve found:

To understand, inform, and influence foreign publics in promotion of the national interest and to broaden the dialogue between Americans and U.S. institutions and their counterparts abroad. To accomplish this, we

• explain and advocate U.S. policies in terms that are credible and meaningful in foreign cultures;

• provide information about the U.S., its people, values, and institutions;

• build lasting relationships and mutual understanding through the exchange of people and ideas; and

• advise U.S. decision-makers on foreign attitudes and their implications for U.S. policies.

A colleague of mine summarized this mission by calling our activities "retail politics on a global scale." The people practicing public diplomacy are the ones disseminating the President’s latest speech on foreign policy, explaining its points to a skeptical local newspaper editor, or writing a speech on the same theme, but adapted to local conditions, for the U.S. Ambassador to give. On another day, the public diplomacy practitioner is helping select candidates for the Fulbright academic exchange program and attending a seminar or cultural event that connects the country where he is posted with the United States. In each case, our practitioner is reaching beyond the government elites who decide policy and is interacting with the larger publics in the country where he or she is serving. He is in touch primarily with influential people, journalists, academics, and other leaders in society who help shape public opinion. He knows people from several age groups and across the political spectrum, including among the opposition - even if the opposition is not in the local government’s best graces.