The newts' skins are dry and velvety when they are living on land, but become smooth when they migrate into the water to breed.

Males develop a more vivid colour pattern and a conspicuous skin seam (crest) on their back when breeding.

The smooth newt was originally described by Carl Linnaeus as a lizard, and was then given different genus names before the adoption of its current classification as a member of Lissotriton.

They can adapt to a wide range of natural or semi-natural habitats, from forests at field edges to parks and gardens.

The smooth newt is abundant over much of its range and is classified as a species of least concern by the International Union for Conservation of Nature (IUCN).

Swedish naturalist Carl Linnaeus described the smooth newt in 1758 as Lacerta vulgaris, placing it in the same genus as the green lizards.

[9]: 233  They used the name Lissotriton, introduced by the English zoologist Thomas Bell in 1839 with the smooth newt as type species[10]: 132  but then considered a synonym of Triturus.

Within the smooth newt itself, genetic groups do not completely match the currently accepted subspecies (ampelensis, meridionalis, vulgaris), described based on morphology.

[2] These patterns are likely due to the range expansion and secondary contact of species after the Last Glacial Maximum, which they likely survived in refugia mainly in southern and eastern Europe.

[11]: 25  Artificial crosses with even more distant species such as the alpine (Ichthyosaura alpestris) and northern crested (Triturus cristatus) newts were successful in laboratory experiments.

The head is longer than it is wide, with 2–3 longitudinal grooves on the top, and the elongated snout is blunt in the male and rounded in the female.

The skin is velvety and water-repellent on land but smooth during the aquatic phase; it contains mucus and toxin glands and its upper layer is shed off regularly.

[11]: 107 During the aquatic breeding season, males develop a skin seam or crest, which runs uninterrupted along the back and the tail.

The cloaca (the single digestive, urinary and reproductive orifice) of breeding males is swollen, round and dark-coloured.

Females only develop low, straight tail fins but no crest or toe flaps, and are more drably coloured.

In the nominate subspecies, L. v. vulgaris, the crest is clearly denticulated, toe flaps are only weakly developed and the body is round.

They initially have, in addition to their gills, only two balancers at the sides of the head, short appendages for attaching to plants which get resorbed within a few days.

The smooth newt was available in the Australian pet trade until 1997, when it was declared a "controlled pest animal" because of the risk of introduction.

They also usually hibernate on land, often in congregations of several newts in winter shelters such as under logs or in burrows (but they can be active during mild weather).

[5]: 238  The newts recognise familiar territory using smell and visual cues, but could not orient themselves in experiments when they were transported far away from the home range.

[25] Migration to the breeding sites occurs as soon as February, but in the northern parts of the range and at higher altitudes, it may not start before summer.

[5]: 238 Mating involves an intricate courtship display: the male attempts to attract a female by swimming in front of her and sniffing her cloaca.

Larvae typically hatch after 10–20 days, depending on temperature, and metamorphose into terrestrial efts after around three months.

[5]: 238–240 Paedomorphism, where adults stay aquatic and retain their gills and skin seams or only resorb them partially, occurs regularly but only in a small proportion of individuals.

It does not appear to be determined genetically but favoured by cold water, a low density of individuals and abundant aquatic prey.

They include especially the loss of breeding ponds through destruction or introduction of fish, and the fragmentation of population through roads.

[11]: 204–205  The value of artificial water bodies as habitat can be improved when nearby hiding structures like stones or wood are added on land.

[36] Garden ponds are readily colonised if they are sun-exposed, have abundant water plants, no fish, and nearby hiding structures.