Bob & Carol & Ted & Alice focuses on four friends who decide to experiment with sexual freedom. After pushing the sexual boundaries with others, the foursome decide they have one last boundary to cross truly to test what they consider their new enlightened state.
Mazursky was lucky to get four such excellent performers working on his project, for the movie lives and dies based on their ability to quietly suggest the inner workings of a human mind.
Like most zeitgeist movies, Paul Mazursky's comedy about mate-swapping quickly became outdated, but it's well acted (by Elliott Gould and Dyan Cannon) and serves as a sociological document to the shifting sexual mores of the late 1960s.
The genius of Bob & Carol & Ted & Alice is that it understands the peculiar nature of the moral crisis for Americans in this age group, and understands that the way to consider it is in a comedy.