The Unbearable Lightness of Beingis a 1988 American film adaptation of the novel of the same name by Milan Kundera , published in 1984.Director Philip Kaufman and screenplay writer Jean-Claude Carrière show Czechoslovak artistic and intellectual life during the Prague Spring of the Communist period, before the Soviet and Warsaw Pact invasion in August 1968, and detail the moral–political effects and personal consequences upon a bohemianménage à trois: a medical doctor and his two women.

The Unbearable Lightness of Beingintroduces Czech brain surgeon Tomas ( Daniel Day-Lewis ), a lothario who is a successful medical doctor in Communist Czechoslovakia. His lover, Sabina ( Lena Olin ), is an equally care-free artist. One day, Dr Tomas leaves Prague to operate on a man in a spa town . There, he meets the waitress Tereza ( Juliette Binoche ), who dreams of escaping her small town life. She follows him to Prague and cohabits with him, complicating Tomas's extra-domestic sexual affairs.

Tomas asks Sabina to help Tereza find work as a photographer. Tereza is fascinated and jealous as she grasps that Sabina and Tomas are lovers. Her distress about his polyamory is interrupted by the Soviet Army tanks invading Czechoslovakia. Amidst the confusion, Tereza photographs the Soviet invasion, then hands the rolls of film to foreigners to smuggle to the West. Facing the stultifying reality that replaced the Prague Spring, Tomas, Sabina, and Tereza flee Czechoslovakia for Switzerland; first Sabina, then the hesitant Tomas and Tereza.

In Geneva , Sabina meets Franz ( Derek de Lint ), a married university professor; they begin a love affair. After some time, he decides to abandon his wife and family for her. After hearing the declaration, Sabina abandons Franz, feeling he would emotionally weigh her down. Meanwhile, Tereza and Tomas attempt to adapt to Switzerland, whose people Tereza finds inhospitable. When she discovers that Tomas continues womanizing, she leaves him and Switzerland, and returns to Czechoslovakia. Upset by her leaving, Tomas follows Tereza to Czechoslovakia, where his passport is confiscated, locking him in-country; nevertheless, his return elates Tereza. They are re-united.

In Prague , Tomas tries recovering his old brain surgeon hospital job, but the Soviet-backed régime consider him politically incorrect and prevent his re-employment. Before the invasion, Tomas wrote an article comparing the Soviets to Oedipus Rex ; noting that Oedipus plucked out his eyes upon understanding his crime, but that the autocracy could see everything but its crimes. The régime demands his signature to a letter repudiating the article. Tomas refuses, and is black-listed from practicing medicine; he works as a window washer, and continues womanizing.

Working as a waitress, Tereza meets an engineer who propositions her. Aware of Tomas's infidelity, she enters a one-time and unpleasant sexual liaison with the engineer. Remorseful, she fears the engineer might have been a secret agent for the régime, who might blackmail her and Tomas. She contemplates suicide, which Tomas thwarts.

Stressed by insubstantial city life, Tereza convinces Tomas to leave Prague for the country; they go to a village where an old patient of Tomas' welcomes them. In the village, they live a farm idyll, far from the political intrigues of Prague. In contrast, Sabina has gone to the US, where she continues in the detached bohemian style of life. Later, Sabina is shocked by the letter telling of the deaths of Tereza and Tomas in a road accident while returning after celebrating in another town. Their lightness no longer unbearable, Tereza and Tomas were deeply happy as they drove toward death.