Abstract
The theory of quantised fields in de Sitter space is investigated. It is demonstrated that de Sitter invariant fields transform like Minkowskian fields under a subgroup of the conformal group, if the de Sitter space is parametrised by horospherical coordinates. Special attention is thus focused on the resolution of the apparent causality conflict. For fields of spin less than or equal to one the field equations are derived; the case of arbitrary spin is dealt with by means of Weinberg-type fields. Furthermore, the author gives an improved version of the renormalisability proof for the model of a quantised scalar particle in the classical de Sitter background field.