The extent of lateral gene transfer among diverse microbes has effectively broken down our concept of species when we seek to apply it to the microbial world. The explosive growth of whole genome sequences for a great number of microbes give us an unprecedented perspective on the entire process of cellular evolution known. The field is rife with controversies, which have been waged fiercely over the past 20 years and which now are all coming to a point of resolution. Sapp has brought together the best workers in this field to assess what we now know, and to try to reach an accommodation and consensus on the broad outline of how cellular life has evolved.