The Unbearable Lightness of Being (Czech: Nesnesitelná lehkost bytí) is a 1984 novel by Milan Kundera about two women, two men, a dog, and their lives in the 1968 Prague Spring period of Czechoslovak history. Although written in 1982, the novel was not published until two years later, in a French translation (as L'insoutenable légèreté de l'être). The same year, it was translated to English from Czech by Michael Henry Heim and excerpts of it were published in The New Yorker. The original Czech text was published the following year. A feature-length film adaptation of the same name was released in 1988.

In 1968, Tomáš, a gifted surgeon in Prague, lives according to a personal philosophy of “lightness”, indulging in numerous sexual encounters without attachment. Previously married, he avoids all contact with his former wife and their young son, Šimon, embracing a life of permanent detachment. During a trip to a provincial town, he meets Tereza, a café waitress. When she later follows him to the capital, he understands that she is essentially entrusting her life to him. As a habitual womanizer, he initially resists his growing affection, but eventually gives in to it.

Tereza, dissatisfied with her existence in her small hometown and eager to escape her coarse mother, sees in Tomáš both an intellectual and a dreamer. She falls for him immediately. They move in together, yet Tomáš continues seeing other women. At first, he conceals his infidelity, but later admits it, insisting that his sexual encounters have no bearing on his devotion to her. Unable to embrace such a separation between love and physical desire, Tereza is plagued by disturbing dreams and sinks into despair, contemplating suicide.

The political liberalization of the Prague Spring ends abruptly in August with the Soviet invasion. Because of a past essay criticizing the ruling regime, Tomáš is warned to flee. In 1969, hoping to secure Tereza’s happiness, Tomáš marries her — but does not abandon his lovers. Among them is Sabina, a talented, free-spirited painter and his closest confidante. Tereza is drawn to Sabina’s openness, and they become friends. Sabina even helps Tereza find work as a photographer in Prague, but the undercurrent jealousy over Tomáš remains.

In 1970, Sabina leaves for the West, and eventually Tomáš and Tereza join her in Zurich, Switzerland. However, Tereza feels purposeless without her photography and grows resentful while Tomáš continues his affairs. Believing that “when the strong are too weak to hurt the weak, the weak must be strong enough to leave”, she returns to Czechoslovakia a year later. Tomáš, after briefly enjoying his regained independence, follows her back later that same year — knowing this means abandoning the possibility of leaving the country again.

However, in Prague, 1972, Tomáš’s political troubles deepen. He refuses to sign a statement retracting his political criticism, costing him his surgical career. Both state authorities and dissident circles attempt to enlist him, but he rejects being used by either. His estranged son, Šimon, now politically active, lectures him to no avail. Seeking anonymity, Tomáš takes work cleaning windows, though his notoriety endures, and he continues his sexual encounters with other women.

In 1973, Tereza, now working as a bartender, has an affair with a visiting engineer in an attempt to emulate Tomáš’s detachment. The experience leaves her feeling worse — convinced the man was a police informant gathering evidence. After much emotional turmoil, she persuades Tomáš to relocate to a rural village, ending his sexual encounters. Life in the countryside brings them tranquility, but their time is cut short when they die together in a sudden car accident the following year.

Meanwhile in Geneva, 1971, Sabina embarks on a relationship with Franz, a married academic whose idealism aligns more with Tereza’s sensibilities than her own. Franz idolizes Sabina, but feels tormented by betraying his wife, Marie-Claude. Sabina, in contrast, views this betrayal as an exhilarating step into the unknown.