Gonepteryx rhamni, commonly named the common brimstone, is a butterfly of the family Pieridae. It lives throughout the Palearctic zone and is commonly found across Europe, Asia, and North Africa. Across much of its range, it is the only species of its genus, and is therefore simply known locally as the brimstone. Its wing span size is 60–74 mm (2.4–2.9 in). It should not be confused with the brimstone moth Opisthograptis luteolata.

The brimstone relies on two species of buckthorn plants as host plants for its larvae; this influences its geographic range and distribution, as these plants are commonly found in wetlands. The adult brimstone travels to woodland areas to spend seven months overwintering. In spring when their host plants have developed, they return to the wetlands to breed and lay eggs. Both the larval and adult forms of the common brimstone have protective coloration and behaviour that decreases their chances of being recognised and subsequently preyed upon.

The adult common brimstone has sexual dimorphism in its wing coloration: males have yellow wings and iridescence while females have greenish-white wings and are not iridescent. This iridescence is affected by environmental factors.

The name "butterfly" is believed to have originated from this species, which was called the "butter-coloured fly" by early British naturalists.

It was first described and published in Linnaeus's book, the 10th edition of Systema Naturae in 1758.

Brimstone is an old name for sulphur, the colour which matches the colour of the male's wings.^{[citation needed]}

The common brimstone can be commonly found throughout the Palearctic. Individuals have been seen from western Europe to east Asia. The high mobility of this butterfly allows it to search widely for new host plant locations and expand its range. While the geographic distribution of the adult is larger than that of its host plant, its range is nevertheless limited by the presence of host plants due to the needs of its larval stage.

The common brimstone uses various environments for different stages of its life cycle. The butterfly inhabits wetlands during mating and breeding season, as they provide ideal areas for oviposition due to an abundance of host plants like the alder buckthorn. The common brimstone prefers laying eggs on younger host plants with late bud-bursts that are isolated from other plants in the area and exposed to both open space and sun. During the winter, adult brimstones travel to woodlands to hibernate, as they provide ideal overwintering sites with shelters such as evergreen foliage and holly. The common brimstone has an appearance that is highly similar to the leaves of these plants, so during hibernation it can remain hidden. In other seasons, habitat selection is also affected by the abundance of nectar as a food source for adult brimstones.