Two years ago we unveiled the genome sequence of crAssphage, the most abundant and ubiquitous phage on the planet. This ~97 kb Bacteroidetes phage is a previously unknown player in the ecology of human intestines and is present in the intestines of approximately half the people in the world. The phage is six times more abundant in public metagenomes than all other known phages together, and in some fecal metagenomes comprises up to 90% of the DNA sequences. The metagenomic evidence suggested that this phage is globally distributed, and so we developed an assay to explore the local and global variation of the phage, and the temporal evolution of the phage. Three amplicons were designed, two of which cover more conserved regions, and a third covers a more variable region. Using samples from Southern California sewage plants we developed a protocol to test for crAssphage, and thanks to collaborators in twenty countries around the world we now have a picture of the spread and evolution of this pandemic phage.