β-N-Acetyl-D-galactosamine (GalNAc) is an amino sugar derived from galactose found in O-linked and N-linked glycans. As an essential sugar, the role is basically the same for N-acetylgalactosamine as it is for the others, which is to enhance cellular communication. Although there has not been much research to date, what has been done reveals that this saccharide may inhibit the growth of some tumors. For example, colon cancer patients have only half the normal amounts of N-acetylgalactosamine. Studies have shown that colon cancer cells that metastasize make more mucin, making them more likely to form metastases. Therefore, it appears that N-acetylgalactosamine plays an important role in preventing this formation from occurring. N-acetylgalactosamine and N-acetylglucosamine glycans is a predictor of metastasis and poor prognosis in a number of human adenocarcinomas, including breast cancer. Lower than normal levels of this sugar has been found in patients with heart disease implying that these conditions may be reversed if a supplementation of N-acetylgalactosamine were to be added to the diet. It appears that β-N-Acetyl-D-galactosamine plays a role in joint function, sweeping away destructive free radicals that can cause inflammation. N-acetylgalactosamine also seems to play an important role in the immune system. Contained in macrophages and neutrophils, it may play a significant role in the etiology of joint inflammation and could be important in such conditions as rheumatoid arthritis. In humans, it is the terminal carbohydrate forming the antigen of blood group A. N-acetylgalactosamine (GalNAc) is a well-defined liver-targeted moiety benefiting from its high affinity with asialoglycoprotein receptor (ASGPR). By conjugating it directly to the oligonucleotides or decorating it to a certain delivery system as a targeting moiety, GalNAc has achieved compelling successes in the development of nucleic acid therapeutics in recent years. Several oligonucleotide modalities are undergoing pivotal clinical studies, followed by a blooming pipeline in the preclinical stage. N-Acetyl-D-galactosamine is used in affinity chromatography, protein chromatography and in carbohydrate matrices. N-Acetyl-D-galactosamine has been used to study periodontal disease and to facilitate the design of potent small-molecule ice recrystallization inhibitors. N-Acetyl-D-galactosamine has also been used to demonstrate a molecular shuttle between extracellular and cytoplasmic space allows for monitoring of GAG biosynthesis.