Marina and Astrov drink tea in the garden of Serebryakov's country house. They talk about how they've known each other for at least eleven years.
Astrov thinks that he has become old and eccentric.
Voynitsky, aka Vanya, comes out of the house after his nap. He complains that ever since Professor Serebryakov and his wife have come to the house to live his schedule has been interrupted.
Marina also notices that the Professor has screwed up the house's eating schedule, and Vanya worries that they'll stay for a hundred years.
Serebryakov, his wife Yelena, his daughter Sonya, and their neighbor Telegin come into the garden from their walk. Only Telegin joins Marina for tea.
Vanya gets in some jabs about how old the Professor is and also moons over how beautiful the Professor's wife is.
Vanya thinks that Yelena should betray her old husband so that she can be true to herself and enjoy her youth. Telegin thinks that's not such a great idea.
Sonya and Yelena come out into the garden, and Mariya, the mother of Vanya and of the Professor's first wife, joins them.
Mariya tries to start talking about a philosophical or political debate that she's been reading, but Vanya cuts her off rudely.
He's jealous of how much his mother admires the Professor and makes vaguely suicidal references.
Astrov, a doctor, is called away to the factory and as he goes Sonya starts bragging about what a great guy he is. It turns out he has earned medals for planting new trees and campaigning against the destruction of old forests.
This really gets Astrov going and he starts on a tirade against the people who are cutting down the trees instead of using peat to burn and building their houses of stone instead of wood.
Sonya leaves to see Astrov to the door, and while they're gone, Yelena scolds Vanya for the way he acted toward his mother and her husband.
Vanya confesses his love to Yelena, and she begs him to stop before someone hears.