The document summarizes Jonathan Eisen's presentation on phylogenomic approaches to studying microbial diversity. Specifically, it discusses rRNA phylotyping which involves extracting DNA from a sample, amplifying the rRNA genes via PCR, sequencing the genes, aligning the sequences to create a data matrix, clustering similar sequences into operational taxonomic units (OTUs), and constructing a phylogenetic tree to visualize relationships between OTUs and identify dominant taxa in a community.