What unites eukaryotic transcription across a billion years of evolution — from animals and plants to algae, fungi, and diverse protists? While some features of the transcription machinery are deeply conserved, tracing back even to archaea, others have diverged dramatically. General transcription factors, for instance, are duplicated or missing in different lineages. Core promoter elements, where the pre-initiation complex binds, are widespread yet have also been lost and reinvented many times. Why such diversity? What are the benefits of gaining or losing these elements or proteins in the basic machinery of transcription? These questions remain unanswered. With the explosion of genomic data and the growing diversity of model organisms across the eukaryotic tree of life, we are now in a unique position to uncover the evolutionary logic of transcription.