The guards on night watch at the royal castle in Elsinore. Some of them have seen the ghost of Hamlet's father. They have invited Horatio, a scholar, to join them and speak to the ghost. Horatio is sceptical. The ghost appears and Horatio tries without success to get it to explain its presence. The men agree to tell Hamlet what they have seen.
Claudius explains why he has married Gertrude so soon after her husband's death. Claudius sends two ambassadors to make peace with the Norwegians about the threat posed by Fortinbras, nephew of the King of Norway. Claudius tries to win Hamlet's friendship. Hamlet reveals in a bitter soliloquy that his mother's marriage to Claudius is the cause of his depressed state. Horatio & Marcellus tell Hamlet about the ghost and decides to go on the guard-platform that night.
Laertes and Ophelia exchange farewells before Laertes leaves for France. Laertes warns Ophelia not to take Hamlet's declarations of love for her seriously. Polonius gives Laertes advice on how he should conduct himself in France. Polonius warns Ophelia about Hamlet and orders her not to see him again. She agrees to obey her father's wishes.