The painting depicts the moment when the god Apollo, identifiable by the crown of laurel on his head, visits Vulcan, who is found making weapons for war. The god Apollo tells Vulcan that his wife, Venus, is having an affair with Mars, the god of war. For this reason, the other figures in the room are looking in surprise at the god who has just appeared before them, some of them even opening their mouths to indicate surprise.

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The subject is taken from Roman mythology, specifically from Ovid's Metamorphoses. Velázquez interpreted the scene into a strictly human version, with contemporary figures. Apollo is seen wearing a toga which leaves his torso exposed to view. Vulcan, in this picture, is just a blacksmith, as are his helpers, who are men from the village who know the trade. Vulcan is staring at him in astonishment after having heard the news of his wife's adultery with the god Mars, for whom he is forging armour at this very moment. The cave in which the blacksmith god forges weapons for the other deities in this painting is shown as a smithy, similar to those Velázquez could have seen in Spain or in Rome. With characteristic mastery Velázquez also painted a variety of objects which would be commonly found in a forge.