Bifidobacteria comprises up to 25% of the cultivable fecal bacteria in adults and 80% in infants. Many in vivo and clinical research results supporting its efficacy in the prevention and improvement of gastrointestinal health have been accumulated. As a consequence, expert committee WHO/FAO expert committee recommended Bifidobacterium as representative probiotics together with Lactobacillus acidophilus. In this review, research trends in bifidobacteria concerning the classification and identification of the genus Bifidobacterium, modulation of intestinal microflora, improvement of constipation, prevention of diarrhea, alleviation of atopy and allergy, barrier function through antimicrobial activity andimmune enhancement of the host will be introduced. Several gene expression systems based on bifidobacterial plasmids have been developed and successfully used to express several heterologous genes including anticancer proteins in Bifidogacterium. In animal test, bifidobacteria was proven to be a promising candidate for safe gene delivery system which can specifically colonize in the solid tumor.