Circulating cell-free DNA is poised to transform cancer diagnosis and care; however, it carries technical challenges such as low abundance, fragmentation and sensitivity to biospecimen handling. Development of clinically useful assays hinges on understanding the unique technical aspects of working with cell-free DNA as a substrate. This book provides an in-depth summary of the technical issues impacting cell-free DNA purification from blood plasma and analysis in a cancer context, including design of PCR assays, sequencing library preparation and methylation analysis. Emerging fields such as extracellular vesicles and blood nucleases are also covered, as well as basic biology and considerations pertinent to biobanking.