Single-stranded DNA (ssDNA) intermediates play an important role in processes such as DNA replication and homologous recombination, DNA damage responses, and DNA repair. Using quantitative amplification of ssDNA (QAOS), ssDNA arising during various cellular processes in complex genomes can be quantified at numerous single-copy and repetitive loci. QAOS is a useful tool to gain insights into the cellular processes that involve ssDNA and the roles of proteins in regulating ssDNA production and responses to ssDNA.