1. C++ introduces three access modifiers - public, private, and protected - to control access to members of a class and establish boundaries in the relationship between a class and its clients. 2. Public members form the class's interface and are accessible by anyone. Private members are the internal workings of the class and are inaccessible to clients. Protected members are accessible by derived classes. 3. The 'friend' keyword allows specific functions or classes to access a class's private and protected members, but friendship is not inherited and overuse of friends is not recommended.