  Human Digital Twins (HDTs) are a fast-emerging technology with significant
potential in fields ranging from healthcare to sports. HDTs extend the
traditional understanding of Digital Twins by representing humans as the
underlying physical entity. This has introduced several significant challenges,
including ambiguity in the definition of HDTs and a lack of guidance for their
design. This survey brings together the recent advances in the field of HDTs to
guide future developers by proposing a first cross-domain definition of HDTs
based on their characteristics, as well as eleven key design considerations
that emerge from the associated challenges.
