Epica performs a blend of progressive metal, gothic metal and symphonic metal. Another component of Epica's style is power metal; their former guitarist Ad Sluijter having described the band as "a bridge between power metal and gothic metal. Vocalist Simone Simons has expressed a preference for the group to be described as symphonic metal though the founder of the group Mark Jansen notes that they do not mind being called gothic metal.
The music of Epica is aggressive, bombastic and excessive with some songs being "epic, grand and majestic" and others "more subdued and introspective. The band is also known to have progressive tendencies while a gothic atmosphere and sentimentality is also present in their music.
Epica uses a "trademark of many symphonic and gothic metal bands" in contrasting "two extremes, death grunts and brutality on one side, airy female melodiousness on the other." Eduardo Rivadavia of Allmusic notes that the band's "attraction ultimately hinges on exploring the sonic contrasts of light and dark; the punishing intensity of those elephantine guitar riffs and hyperactive drumming cast against the soaring, layered sweetness of the orchestrated strings and keyboards." Simone Simons delivers operatic vocals in a mezzo-soprano range though she has also been known to sometimes sing "with a clear alto voice that has a flawless tone and a lot of emotion." Mark Jansen delivers death grunts "that are secondary to Simons' singing, but very important in terms of balance and variety." The group is also known to employ human choirs and orchestras with additional embellishments such as spoken word recitals and lyrics in Latin and Arabic.
