Several methods, including whole genome bisulfite sequencing (WGBS) and reduced representation bisulfite sequencing (RRBS), are currently used for genome-wide DNA methlyation analysis. These methods convert unmethylated cytosines to uracil while 5-methylcytosines remain unchanged by the bisulfite treatment. This allows epigenetic differences to become genetic differences, which can be subsequently detected via sequencing at the single-based resolution level and on a genome-wide scale. However, practical use with such current methods are not ideal as they (1) need large amounts of DNA (>1 µg) as input material, which is difficult to prepare from limited biological samples such as tumor biopsy, early embyros, embyronic tissues, and circulating DNA; (2) require DNA to first be sheared and then ligated to adapters, followed by bisulfite conversion (post-ligation bisulfite conversion), which causes substantial amounts of DNA fragments contained in the adapter-DNA fragment constructs to be broken and thereby forms mono-tagged templates that become removed during library enrichment; and (3) are time-consuming (2 days). The Post-Bisulfite DNA Library Preparation Kit (For Illumina®) is designed to overcome these weaknesses.