The common toad, also known as European toad or simply the toad in Anglophone parts of Europe (Bufo bufo, from Latin bufo "toad"), is a toad found throughout most of Europe (excluding Iceland, parts of Scandinavia, and some Mediterranean islands), western North Asia and a small part of Northwest Africa. It belongs to a group of closely related species descended from a common ancestral line of toads and forming a species complex. The toad is an inconspicuous animal, usually lying hidden during the day. It becomes active at dusk, hunting the invertebrates on which it feeds at night. It moves with a slow, ungainly walk or by jumping short distances, and has greyish-brown skin covered with wart-like lumps.

Although toads are usually solitary animals, large numbers of them converge on certain breeding ponds during the breeding season, where the males compete to mate with the females. The females lay their eggs in gelatinous strings in the water, which later hatch into tadpoles. After several months of growth and development, the tadpoles sprout limbs and undergo metamorphosis to become tiny toads. The juveniles then leave the water and remain largely terrestrial for the rest of their lives.

The common toad appears to be in decline in some areas, but is currently classified as being of "least concern" on the IUCN Red List of Threatened Species. It is under threat due to habitat loss, particularly the drainage of its breeding grounds, and some toads are killed on roads during their annual migrations. The toad has long been associated with witchcraft in popular culture and literature.

The common toad was first given the name Rana bufo by the Swedish biologist Carl Linnaeus in the 10th edition of Systema Naturae in 1758. In this work, he placed all the frogs and toads in the single genus Rana. It later became apparent that this genus should be divided, and in 1768, the Austrian naturalist Josephus Nicolaus Laurenti placed the common toad in the genus Bufo, naming it Bufo bufo. The toads in this genus are included in the family Bufonidae, the true toads.

Various subspecies of B. bufo have been recognised over the years. The Caucasian toad is found in the mountainous regions of the Caucasus and was at one time classified as B. b. verrucosissima. It has a larger genome and differs from B. bufo morphologically and is now accepted as Bufo verrucosissimus. The spiny toad was classified as B. b. spinosus. It is found in France, the Iberian Peninsula and the Maghreb and grows to a larger size and has a spinier skin than its more northern counterparts with which it intergrades. It is now accepted as Bufo spinosus. The Gredos toad, B. b. gredosicola, is restricted to the Sierra de Gredos, a mountain range in central Spain. It has exceptionally large paratoid glands and its colour tends to be blotched rather than uniform. It is now considered to be a synonym of Bufo spinosus.

B. bufo is part of a species complex, a group of closely related species that cannot be clearly demarcated. Several modern species are believed to form an ancient group of related taxa from preglacial times. These are the spiny toad (B. spinosus), the Caucasian toad (B. verrucosissimus) and the Japanese common toad (B. japonicus). The European common toad (Bufo bufo) seems to have arisen more recently. It is believed that the range of the ancestral form extended into Asia but that isolation between the eastern and western species complexes occurred as a result of the development of the Central Asian Deserts during the Middle Miocene. The exact taxonomic relationships between these species remains unclear. A serological investigation into toad populations in Turkey undertaken in 2001 examined the blood serum proteins of Bufo verrucosissimus and Bufo spinosus. It found that the differences between the two were not significant and that therefore the former should be synonymized with the latter.

A study published in 2012 examined the phylogenetic relationships between the Eurasian and North African species in the Bufo bufo group and indicated a long evolutionary history for the group. Nine to thirteen million years ago, Bufo eichwaldi, a recently described species from south Azerbaijan and Iran, split from the main lineage. Further divisions occurred with Bufo spinosus splitting off about five million years ago when the Pyrenees were being uplifted, an event which isolated the populations in the Iberian Peninsula from those in the rest of Europe. The remaining European lineage split into Bufo bufo and Bufo verrucosissimus less than three million years ago during the Pleistocene. Very occasionally the common toad hybridizes with the natterjack toad (Epidalea calamita) or the European green toad (Bufotes viridis).

The common toad can grow to around 15 cm (6 in) in length. Females are usually stockier than males, and southern specimens tend to be larger than northern ones. Its head is broad, with a wide mouth below the terminal snout, which has two small nostrils. There are no teeth. The bulbous, protruding eyes have yellow or copper-coloured irises and horizontal, slit-shaped pupils. Just behind the eyes are two bulging regions: the paratoid glands, which are positioned obliquely. These glands secrete a noxious substance called bufotoxin, which is used to deter potential predators. The head joins the body without a noticeable neck, and there is no external vocal sac. The broad. squat body is positioned close to the ground. The forelimbs are short, with the toes of the front feet turning inwards.