Probiotic products constitute one of the most successful segments of the functional foods market. Recent regulations developed in different countries require extensive documentation from human studies before a health claim can be approved for a food product. This gives a new direction to this research area and underlines the need for products with a high functional efficacy. Most of the current probiotic products target the general population, whilst those formulated for specific human groups are still lacking. Some individuals or patient groups present particular nutritional needs and require nutritionally adapted products, thus constituting an opportunity for the development of specifically formulated foods. In this context, it is critical to identify both the target populations that may benefit the most from such products, and the specific probiotic properties that fulfil the requirements of such populations. Human groups that can benefit from this joint development include groups of extreme age and patients suffering from diseases in which intestinal microbiota and/or immune modulation may have beneficial effects. The development of such target-specific probiotic foods, by including strains rationally selected for a specific health benefit, tailor-made for a certain target population, into nutritionally optimal products constitutes a challenge for the food industry.