Abstract
Over the past two decades, it has become clear that the multi-scale spatial and temporal organization of the genome has important implications for nuclear function. This chapter centers on insights gained from recent advances in light microscopy on our understanding of transcription. Particular focus is given to the genomic scales where most functional interactions occur, namely kb-Mb. We discuss the relevant spatial and temporal scales that shape nuclear order and their consequences on regulatory components and function. The emerging picture is that spatiotemporal constraints increase the complexity in transcriptional regulation. This brings new challenges to the fore, such as uncertainty about how information travels from factors through the genome and space to generate a functional output.