Gene expression involves a cascade of events, from transcription factor transactivation and RNA polymerase binding to RNA processing and maturation. mRNA profiling has yielded a vast amount of information about the total RNA content in different tissues physiological states. However, it has been unclear how the variable amounts of mRNA might correlate with transcriptional events. Recent advances in single-cell imaging offer a platform for 'cellular genomics', the high throughput analysis of transcriptional activity in single cells.