let g be a simple and simply connected algebraic group over a field. we can attach to a it the sheaf of conformal blocks: a vector bundle on $m_g$ whose fibres are identified with global sections of a certain line bundle on the stack of g-torsors. we generalize the construction of conformal blocks to the case in which g is replaced by a ``twisted group'' defined over curves in terms of covering data. in this case the associated conformal blocks define a sheaf on a hurwitz stack and have properties analogous to the classical case.