The use of lactic acid bacteria (LAB) in different food products has been driving the consumer market due to the potential probiotic action of these bacteria, which raises the foods to the status of functional foods. A selection of potential probiotic strains can be obtained from different food matrices and environments. However, these microorganisms must be confirmed as safe while retaining characteristics that make them technologically, functionally and physiologically capable of benefitting the food and health of the host. Characterisation of a potential probiotic strain should include knowledge of the source, pathogenicity, infectivity, virulence factors, viability during processing, storage stability, phage resistance, contribution to sensory properties, tolerance within the gastrointestinal tract, cell adhesion, antimutagenic, anticarcinogenic and antagonistic activity against gastrointestinal pathogens and immunomodulation. Desirable physiological effects of probiotic strains include aiding in lactose intolerance and prevention and reduction of diarrhoea, inflammatory bowel disease and allergies. In this context, this paper reviews the current literature referring to principal criteria for the selection of LAB for potential use as probiotics in foods.