The genus Lactococcus comprises twelve species, some known for decades and others more recently described. Lactococcus piscium, isolated in 1990 from rainbow trout, is a psychrotrophic lactic acid bacterium (LAB), probably disregarded because most of the strains are unable to grow at 30°C. During the last 10 years, this species has been isolated from a large variety of food: meat, seafood and vegetables, mostly packed under vacuum (VP) or modified atmosphere (MAP) and stored at chilled temperature. Recently, culture-independent techniques used for characterization of microbial ecosystems have highlighted the importance of L. piscium in food. Its role in food spoilage varies according to the strain and the food matrix. However, most studies have indicated that L. piscium spoils meat, whereas it does not degrade the sensory properties of seafood. L. piscium strains have a large antimicrobial spectrum, including Gram-positive and negative bacteria. In various seafood, some strains have a protective effect against spoilage and can extend the sensory shelf-life of the products. They can also inhibit the growth of Listeria monocytogenes, by a cell-to-cell contact-dependent. This article reviews the physiological and genomic characteristics of L. piscium and discusses its spoilage or protective activities in food.