Biological therapies in inflammatory bowel disease reflect the exponential advancement in understanding the human intestinal immune system and particularly the biology of intestinal inflammation during the past decade. The better understanding of the mechanisms of inflammatory bowel disease has evolved from desriptive clinical data and genetically engineered animal models. It led to great interest in the evaluation of a variety of new therapeutic agents with novel actions. This review will discuss the mechanisms of biologicals (antibodies against pro-inflammatory cytokines, T cell antibodies, anti-inflammtory cytokines, adhesion molecule blockers, growth factors, hormones, colony stimulating factors, fusion proteins, anti-sense oligonucleotides, trefoil peptides, immunostimulatory [ISS] DNA) used in the treatment of inflammatory bowel disease and summarizes the available data on established biologic therapies as well as investigational agents and briefly touch on probiotics. Based on the data discussed, it seems that biologicals will play an important role in managing inflammatory bowel disease in the near future.