He began his career in the 1930s but really began to make a name for himself in the 1950's. While his peers made gritty, immediate neo-realist films focusing on social issues and the struggles of the poor, Antonioni used film to examine the space between bourgeois characters with a highly refined and stylized directorial aesthetic.
In 1960 he released L'Avventura starring the iconic Monica Vitti. It was a radical departure from European film before it. The film remains an amazing depiction and evocation of alienation and dread. Its title is seemingly ironic (although "avventura" also means "fling," apparently, in addition to "adventure").
His subjects were almost always aimless, wealthy and unhappy. The films invariable had very long takes, minimal dialog and a surface that prevents the viewer from coming up with easy answers to Antonioni's implied questions. L'Avventura and his subsequent films practically filled the screen with emptiness. Il Deserto Rosso (1964), his first color film, remains one of the bleakest and most beautiful films I've ever seen. I'm sure Criterion will "present" it in the months to come. It also has one of Giovanni Fusco's best scores, mostly consisting of disconcerting electronic beeps and belches (and silence), not to mention amazing Carlo Di Palma's amazing and ground-breaking cinematography.