Heraldium is an online resource dedicated to heraldry, bringing together illustrations and written descriptions of coats of arms, known as blazons, with information about their owners and histories. Its articles also explore heraldic connections to specific places and examples displayed at locations such as churches, castles, civic buildings and houses. The site focuses primarily on British heraldry, while also covering heraldic traditions and practices from other nations.

Heraldium organizes its material into collections on heraldic places, armorials and individual families or people. Featured armorials include those of nations, British royalty, Swansea, universities and colleges, and Welsh local authorities. Its entries cover civic and historic subjects, including Swansea Council and the City and County of Swansea, as well as notable families and individuals associated with Swansea, Hereford and other locations. Examples include the Vivian, Dillwyn, Bird and Bath families, and Sir Matthew Craddock. Visitors can also consult broader heraldry links. Overall, Heraldium serves as a reference and discovery resource for people interested in coats of arms, their historical context and their presence across communities and buildings.