The discovery of metabolite-sensing RNA domains with gene regulatory functions, so-called riboswitches, has greatly expanded our view of the structural and functional complexity of RNA. Hitherto, more than 20 distinct riboswitch classes have been identified, which respond to a variety of small molecules and perform sophisticated gene regulatory tasks. Riboswitches are typically positioned in the 5' untranslated region of bacterial mRNAs, where they control gene expression by transcriptional or translational attenuation. However, the recent investigation of additional riboswitch classes has revealed a more complex repertoire of regulatory mechanisms. This also includes splicing control in filamentous fungi, green algae and higher plants by thiamin pyrophosphate-binding riboswitches, the only class of metabolite-sensing RNAs identified in eukaryotes so far. All eukaryotic riboswitches characterized to date modulate, in a first step, splicing, but the downstream processes under control vary fundamentally among different species further highlighting the versatility of this gene regulatory mechanism.