Melodic metalcore is a fusion genre, that refers to multiple different styles of metalcore.
Firstly, the most popular one is heavily influenced by melodic metal genres such as Melodic Death Metal and Thrash Metal, with bands adopting riffs heavily inspired by At The Gates' 1995 album Slaughter of the Soul. Massachusetts-area bands such as Shadows Fall, Unearth, and Killswitch Engage are often considered as pioneers of this style. On the Melodeath side of Melodic Metalcore, you have bands such as All That Remains, Parkway Drive, and I Killed the Prom Queen and on the Thrash side of Melodic Metalcore you have bands like Bullet for My Valentine, Killswitch Engage, and Trivium. This style is sometimes referred to as "Gothencore", or jokingly as At the Gates-core.

Secondly, there are bands that heavily use elements of post-hardcore, pop rock, post-grunge, and alternative metal. to an extent, consequently making their categorization as metalcore being arguable by some. This style is sometimes referred to as "arena metalcore" due to their commercialized and somewhat anthemic nature. They utilize subtle electronic music elements, sing-along choruses, Linkin Park-esque clean vocals, and melodic riffs with polished production. Examples include later Bring Me the Horizon, Blessthefall, and Memphis May Fire.

Finally, there is a niche of traditional metalcore bands that are not necessarily influenced by melodic death metal, but nevertheless still being highly melodic, with Strongarm, Shai Hulud, From Autumn to Ashes, and Poison the Well being notable examples. These bands sometimes use straightforward melodic riffs and passionate sounding vocals, often derived from emo and screamo. This style of metalcore is often sometimes referred to as Emo Metalcore