For the subject see Ovid, 'Metamorphoses' (1). Daphne, pursued by Apollo, cries for help to her father, the river God Peneus. He transforms her into a laurel bush as Apollo reaches her.
The fresco (transferred to canvas) comes from a series painted in the Stanza di Apollo in the garden pavilion of the Villa Aldobrandini, Frascati.
A fine compositional study in pen and ink survives (Windsor, Royal Collection). While the landscape is the finest in the series and was probably made by Domenichino himself, the authorship of the figures is less secure and may have been assigned to an assistant.