Act I begins with an overture that offers some narrative details about Reverend Parris; the town of Salem, Massachusetts; and the lives of Puritans in the late seventeenth century.

The scene opens with Reverend Parris praying and weeping next to the bed where his daughter, Betty, remains unmoving. Tituba, Parris's slave, enters, and Parris immediately begins yelling at her. Abigail Williams (Parris's niece) enters next and announces that Susanna Walcott has come from the doctor's house. She doesn't come with very good news: according to Susanna, the doctor can't find any natural cause to explain Betty's illness (the implication being that her illness may be supernatural). Eager to protect his reputation, Parris is adamant that nothing sinister or unnatural has occurred.

Susanna leaves, and Abigail says it's rumored that witchcraft is the cause of Betty's illness. Parris is suspicious of Abigail because, earlier, he caught her dancing in the woods with some other girls. Abigail admits to dancing but insists that their activities had nothing to do with witchcraft. Parris explains that some community members want nothing more than to see him gone. If rumors spread that members of his household might be partaking in forbidden activities—like dancing and witchcraft—he might lose his position in the town. Parris also inquires about Abigail's chastity, noting that there have been rumors about her recent dismissal from her position in the Proctor household. Abigail vehemently defends her good name and blames her departure on Elizabeth Proctor's cruel nature: "It's a bitter woman, a lying, cold, sniveling woman, and I will not work for such a woman!"

Ann and Thomas Putnam then enter the room. Their daughter Ruth has also come down with a mysterious illness, and they are convinced that this sickness is the work of the devil. Parris reveals that, as a precaution, he has called for Reverend Hale—who is experienced in catching witches—to confirm that witchcraft is not present in Salem. At this point, the narrator interjects to inform the reader that Thomas Putnam is a greedy and vindictive man. As the conversation continues, Ann Putnam admits that she tried to have Tituba conjure the spirits of the dead to find out why all seven of her babies have died. Disturbed by this information (and concerned for his reputation), Parris once again accuses Abigail and the other girls of practicing witchcraft in the forest. At this point, Mercy Lewis, the Putnams' servant, enters.

The Putnams and Parris leave, and Abigail and Mercy are left alone with Betty. Mercy confirms that Ruth is sick as well and suggests beating Betty as a way to cure her. Another girl, Mary Warren, enters the room, and their panicked conversation makes it clear that more than just simple dancing took place in the woods. Betty wakes up and calls for her mother. Bluntly, Abigail says that her mother is dead, and Betty runs to the window, opens it, and tries to fly to her. From Betty, the audience learns that Abigail drank blood in the woods (as part of a charm to kill Elizabeth Proctor). The girls collectively worry about the consequences should anyone accuse them of participating in witchcraft. Abigail takes charge and tells them what their story is going to be: the girls danced, and Tituba contacted Ruth's dead siblings. She threatens terrible revenge on any of the girls who dare to say anything more.