Formed as a symphonic metal band with gothic tendencies, later Epica have incorporated into their sound strong death metal influences. Starting from the third album, even progressive metal attitudes have become evident. In addition, the band often uses thrash metal and groove metal riffs, black metal passages (mostly in the drum technique), power metal moments and references to Arabic music. Some songs also have electronic shades, dent transitions and folk metal melodies derived from middle eastern, Chinese and Celtic traditions.

Epica is also known for the attention to the vocal lines that, in contrast to the heavy context, weave very catchy, easy to hold, sophisticated and emotional melodies. In the band's sound the use of female vocals and male growls, performed by Simone Simons and Mark Jansen respectively, is fundamental. They primarily write their own lyrics, which often deal with philosophical, psychological, spiritual, moral, scientific, environmental, socio-political, global and topical and personal themes. Epica is also known for their wide use of orchestra and opera choirs.