Public relations aims to achieve effective relationships with audiences to manage an organization's image and reputation. PR differs from advertising in that it is less controlled by the organization and aims to build credibility rather than directly persuade. Successful PR requires identifying key publics, understanding their opinions, and managing the organization's image and reputation over time. Common PR tools include news releases, events, and publications. PR effectiveness is measured through outputs like media coverage and outcomes like achieving goals. Marketing PR can add value by building excitement, introducing products, and demonstrating corporate social responsibility.