Lactobacillus is the bacterial genus that contains the highest number of characterized probiotics. Lactobacilli in general can utilize a great variety of carbohydrates. This characteristic is an essential trait for their survival in highly competitive environments such as the gastrointestinal tract of animals. In particular, the ability of some strains to utilize complex carbohydrates such as milk oligosaccharides as well as their precursor monosaccharides, confer upon lactobacilli a competitive advantage. For this reason, many of these carbohydrates are considered as prebiotics. Genome sequencing of many lactobacilli strains has revealed a great variety of genes involved in the metabolism of carbohydrates and some of them have already been characterized. In this review, the current knowledge at biochemical and genetic levels on the catabolic pathways of complex carbohydrates utilized by lactobacilli will be summarized.