Benjamin (played by Dustin Hoffman in the film), a recent college graduate with no well-defined aim in life, is seduced by Mrs. Robinson (played by Anne Bancroft) and then falls in love with her daughter Elaine (played by Katharine Ross).
Some scenes and themes in the film have become deeply embedded in the popular consciousness, even decades after its release, and have been widely parodied. One such scene involves the one-word career advice given to Benjamin by family friends -- "Plastics", "Aggregates", etc -- offered as a self-explanatory key to a certain life of corporate success.
Warning: Wikipedia contains spoilers
In the famous conclusion of the film, Benjamin makes a desperate drive to somehow head off Elaine's wedding. He arrives just as the bride and groom are exchanging vows, and stands looking down at the couple from an upper window. His screams of "Elaine! Elaine!" at first seem merely pathetic, but when Elaine gives a return cry "Ben!" all hell breaks loose.
After a violent struggle with a large cross, Ben and Elaine run away, and escape on a public bus. The escaping couple sits smiling at the back of the bus, the other passengers stare at them in mute disbelief, and the movie closes with a shot through the back window of Ben and Elaine's smiles fading to an enigmatic neutral expression, and Simon and Garfunkel's soundtrack. This scene has been parodied many times, for example in Wayne's World and The Simpsons.
The film is consistently in the Internet Movie Database's top 250 films, ranked #9 on the American Film Institute's list of 100 Years, 100 Laughs, and has been selected for preservation in the United States National Film Registry.