As RNA polymerase II leaves a gene promoter to transcribe the coding region, it faces a major obstacle - nucleosomes tightly wrapped into chromatin. Mechanisms to deal with this obstacle clearly exist in cells, as transcription through chromatin is very efficient in vivo, whereas nucleosomal templates pose a considerable problem for polymerase progression in reconstituted in vitro systems. Advances in our understanding of transcriptional elongation through chromatin have been made possible recently by the identification of several accessory factors that assist polymerase in the process. Insights into the function of these factors have been gained by a combination of yeast genetics and biochemical studies in mammalian systems.