As a result of the growing presence of foreign immigrants settling in Italy, recent years have seen a significant increase in the number of mixed unions. However, little research has been carried out on the subject in this country, in part due to insufficient availability of suitable data. The aim of this study is to investigate the “market” of formal and informal mixed unions and to understand whether ethnic origin contributes a new element to the marriage/union market, and to verify the applicability of the “exchange theory” to the Italian context. We analyzed a particular segment of the marriage market - mixed parental couples included in the 2005 Sample Surveys of Births. The results showed a clear gender divide in the ethnic preferences of Italian spouses, a high rate of previous marital experience for both Italian and foreign people in mixed pairings, and a high frequency of unmarried and casual mixed relationships. Compared with endogamous couples, the foreign male or female spouse/partner in mixed couples is young and more educated relative to the Italian partner, but is less present in the work market and, when employed, often occupies a less well-qualified position. The “informal union market” works in very similar ways to the “marriage market”; the slight attenuation of relationships observed in the former being attributable to the lesser degree of security guaranteed by an unofficial union. Therefore, the mechanism of mate selection implies that foreigners' appreciated qualities such as youth and high education may be offered in exchange for economic security, upward socio-economic mobility and access to the social network of the native partner: this is a variant of the exchange theory that was found to apply well to transnational marriages/unions in Italy.