Digital PCR is a nucleic acid molecule counting method with unprecedented resolution, relative sensitivity and accuracy. The template is diluted to such an extent that on average 1 template molecule is present in a PCR reaction, and many different small reactions are run in parallel. By counting the number of positive and negative reactions (hence the term ‘digital’) at the end of the PCR, it is possible to determine the starting number of template molecules in the sample under investigation. In other words, the question of how much nucleic acid target molecules are present in a particular sample is answered by measuring how many miniaturized reactions are positive if template is extremely diluted. Importantly, a Poisson correction needs to be applied on the counts, to correct for the fact that some reactions may contain more than 1 template molecule.