Author Summary Transcription, the process of converting DNA into RNA (which in turn is translated into proteins by ribosomes) is carried out by the multisubunit RNA polymerase (RNAP) enzyme. Transcription is fundamental to all organisms across the three kingdoms of life—Eukarya, Bacteria, and Archaea—and can be divided into three major steps: initiation, transcription/elongation, and termination. Eukaryotes have three different nuclear RNAPs, whereas Archaea and Bacteria have one. Archaeal transcription is similar to that of eukaryotes, but initiation requires only two accessory proteins bound to DNA: transcription factor B (TFB) and TATA-box binding protein (TBP). It is believed that studies of the archaeal enzyme may shed light on the more complex eukaryotic RNAP. Our complete structure of the archaeal RNAP from Sulfolobus shibatae has fully elucidated its architecture, confirming its close evolutionary relationship with the eukaryotic RNAP II and at the same time revealed a new subunit, Rpo13, with no ortholog in the eukaryotic enzyme. The location and topology of Rpo13 allow us to suggest a mechanism by which Archaea bypass the additional eukaryotic cofactors required for transcription initiation.