The motherhood pay gap measures the pay gap between mothers and non-mothers, the latter defined in most econometric studies as women without dependent children. It also measures the pay gap between mothers and fathers. This is different from the gender pay gap, which measures the pay gap between all women and all men in the workforce. While there is a considerable international literature on the motherhood gap, differences both in methodologies and in how mothers, non-mothers and fathers are defined using available data create difficulties in comparing estimates. Moreover, in many countries, the data are often unsuitable for analysis, typically because the questions posed in surveys make it difficult to establish the identity of a child’s mother or father (particularly in developing countries where the nuclear family is less common). Nevertheless, many studies draw on international harmonized pay and employment data which provide a useful basis for cross-country comparison, and others provide informative trend analyses for single countries.