A Wizard of Earthsea describes the adventures of Ged, a boy from an obscure village on the Isle of Gont. When raiders come to his village, he weaves a spell to bring down fog, confusing them and saving the village. This draws the attention of Ogion the Wizard, who takes the boy as an apprentice after giving him his name.

A person's name is their most closely held secret, it can be used to gain power over them, and so people have two names, their true name that is given to them by one of power, and their use-name. Ged's use-name is Sparrowhawk, for the birds of prey that he calls from the sky.

Ged is disappointed while living with Ogion, who is a silent and peaceful man. He feels that he is not learning anything exciting. While gathering herbs one day in a meadow, he encounters a pale-skinned girl, who goads him into boasting. She mocks him and Ged decides to learn something to impress her.

That night, he opens the spell book of Ogion, and chances on a spell for raising the dead. To his horror, he realises he has been reading in the dark, and there is a darkness near the door, whispering. Ogion enters and drives away the darkness, and offers Ged the choice, to remain with Ogion in the mountains or go to the school on Roke and learn there.

Ged goes to Roke, and finds that he has a natural talent for magic. Yet he has a rival, an older boy called Jasper, who always seems to make him feel inferior. Ged's only friend is Vetch, a kind and sensible boy from the Isle of Iffish.

One night the tension between Jasper and Ged comes to a head, and they go to the hill above the school to compete. Ged tries to raise the dead, but something else comes out, a darkness that claws at his face. The only one who doesn't flee is Vetch, who reaches out to Ged to help, but before he can wrestle with the creature, the Masters of Roke arrive.

They sensed the power being used and came, and the spells which protect Roke helped them drive it away. Ged takes months to recover, and even then, he not as comfortable with his power as he was. He sees his own pride as having unleashed a great evil on the world, and now learns only to try and defeat it. His confidence in himself is gone.

One night Vetch comes to him, he is about to leave to go home. Ged can barely face him, yet Vetch gives him a great gift, he tells Ged what his true name is. The trust that Vetch has placed in him restores him somewhat.

When he finishes his studies, he goes to a tiny village to live. They would not normally need a Wizard, but a dragon has hatched young on a nearby Isle, and they may need protection. Ged strikes up a friendship with a fisherman there, and learns how to sail without magic, and how to build boats.

One night the fisherman's son is ill, dying, and they fetch Ged to help. Ged sees that the child is dying, and knows that he should not interfere when a spirit is leaving, yet he sees the fisherman's faith in him and strikes out after the spirit.

He enters the dry land of the dead, and realises the he must turn back or he will die too. He walks slowly back toward the wall between the living and the dead. When he reaches the wall, he sees the creature of darkness which had attacked him, waiting there for him. He knows if he returns to the world, it will come to him. He raises his Wizard's staff and leaps at it.

When he returns to the waking world, he knows that remaining in the village will endanger them, and seeks permission to go and deal with the dragons at their source, so that he will be free of his obligation.

He sails to the Isle where the dragons live. He calls on the eldest dragon, but only the younger ones come out, he kills five and wounds another before the great dragon speaks. Ged threatens it with it's true name, because he guessed it was the same dragon from an old tale. It tries to bargain, offering him the name of the creature of darkness, but he binds it to never fly against the Islands.

Ged is free to leave the village, and more, he knows now that the creature has a name, which he was not sure of before.

He decides to return to Roke, but when the ship tries to come close to Roke, it is driven back repeatedly by wind. Ged knows that this means the spells of protection around Roke are driving him away, and that the creature is close.

Instead he goes north, and disembarks with one of the sailors. As they walk along, Ged becomes useasy, and finally the sailor attacks him. It is no longer a man, but a Gebbeth, eaten inside by the creature and taken over by it. It tires to take hold of Ged, to take over his body, but he runs. It follows, but cannot quite catch him. He stumbles into a fortress and safety.

In the fortress is a pale-skinned woman who is married to the Lord. She tells Ged that there is a stone of power which only he can control, that he should touch it and it will tell him the name of the thing following him. He sees the trap, that after touching the stone it would own him, and escapes, fleeing the servants of the stone by changing form into an eagle and flying across the sea.

He makes it to Gont, and finds Ogion, who changes him back into a man. The danger in staying too long in another form is that they may forget that they are a man, and never come back to their own form. Ogion is able to call him back because he knows Ged's true name.

They discuss the creature, and Ged admits he is frightened of it. He fears that it will take him and he will become a Gebbeth, and that the creature will use his power for great evil. Ogion believes that he must take the initative, that he must hunt the creature instead of being hunted.

Ged goes down to the sea and acquires a boat, and goes hunting. When he sees the creature coming to him across the ocean, it pauses, then turns and flies away from him. He pursues it, but comes aground on a tiny island.

There are two old people there, who are terrified of him. The old woman shows him a little dress, covered in pearls, and gives him a crescent of silver to keep. He realises they are probably from a royal family, cast adrift when children, meant to die. They have lived alone on the island forever.

He repairs his boat and continues to pursue the creature. He comes to the isle of Iffish, and finds his friend Vetch. Vetch insists that he should accompany Ged in his quest and they sail on together.

They go past all the known islands, into a place far away from charted areas. Finally they reach a strange place, where the waves look like sand, and Ged steps out of the boat onto the shore. He walks toward the creature, which is waiting for him, and when they come together, he says it's name, which is his own.