The main principle of digital PCR is that a single sample is split into many fractions, all of which are subsequently analysed by a standard PCR method (Figure 1). The sample is fractionated by the simple process of dilution so that each fraction contains approximately one copy of DNA template or less. By isolating individual DNA templates this process effectively enriches DNA molecules that were present at very low levels in the original sample. Therefore, this method has applications for the detection of DNA mutations (or any other DNA/RNA targets) that are present at very low levels relative to a high background of normal DNA, for example the early stages of cancer development. The other major feature of digital PCR is that data are recorded as positive or negative (i.e. generation of an amplification product or not). Hence, the individual readout signals are qualitative or ‘digital’ in nature.