A billion years ago, a single-celled eukaryote engulfed a cyanobacterium—an organism capable of converting the sun's energy into food in the form of carbohydrates. In one of the single most pivotal events in the history of life, instead of the bacterium being digested, an endosymbiosis was formed, with the bacterial cell persisting inside the host eukaryote for millennia and giving rise to the first photosynthetic eukaryotes. The descendants of this merger include plants, as well as a large number of single-celled eukaryotes that are collectively referred to as algae (i.e. kelp, nori). The remnants of the cyanobacterium eventually evolved into an organelle known as a plastid or chloroplast, which allows photosynthetic eukaryotes to produce their own food—and thus to provide food to animals like us. Despite the importance of this event, a variety of aspects of plastid evolution have long remained shrouded in mystery. In a review in Genome Biology and Evolution, Shannon Sibbald and John Archibald highlight emerging genome data in this field and provide new insight into plastid evolution.