The nuclear receptors (NRs), an important protein superfamily of transcription factors found in all animals, regulate the expression of genes in a large array of biological processes. Their involvement in moulting and metamorphosis, embryonic development, cell differentiation and reproduction of arthropods is well documented. Especially the two NRs that form the functional ecdysteroid receptor and which are at the base of the ecdysteroid signalling cascade regulating moulting and metamorphosis, EcR and USP, have been researched intensively. During evolution, gene duplication and gene loss events have created a broad diversity of these NRs between different groups in the animal kingdom. However, in 2008, at the time this PhD research started, the information that was available on arthropod NRs was mainly restricted to holometabolic insects. Complete sets of NRs for other groups, including Crustacea, Chelicerata or more basal insects were unavailable. Over the last few years, the number of genome sequencing projects that are carried out for Arthropoda is rapidly increasing. This gave us the opportunity to investigate the NRs in a number of other arthropods and compare the sets of NRs between some of these groups. We chose three species, the hemimetabolic pea aphid Acyrthosiphon pisum, the holometabolic buff-tailed bumblebee Bombus terrestris and the chelicerate two-spotted spidermite Tetranychus urticae as representatives of their respective clades. The main research questions that were addressed in the PhD thesis were: (1) Do holometabolic, hemimetabolic and non-insect arthropods exhibit important differences in their sets of nuclear receptors?, (2) What are the consequences towards the ecdysteroid signalling cascade and can any differences be found there?, and (3) Can RNAi be used to add functional information to the fundamental data that these genome annotation analyses have delivered?