The nasal drug delivery system is one of the fastest growing healthcare sectors, with the market expected to be worth $30 billion by 2010. Nasal delivery provides advantages over other methods by allowing for lower doses with fewer side effects and rapid onset of action. Drugs commonly administered nasally include beta-agonists, corticosteroids, antibiotics, and vaccines. Formulations must consider physiological factors like metabolism and toxicity as well as properties like particle size, pH, concentration, and lipophilicity to optimize absorption. The nasal route is well-suited for delivery of non-peptide drugs and peptides like insulin.