Coating technique is useful to improve the physical, chemical and biological stability and protects the drug against environmental factors. The insoluble drugs are often presented in the form of amorphous solids which may undergo crystallization over time to attain most stable form. To retain the drug in amorphous form i.e., most soluble form and to inhibit surface crystallization, the amorphous form may be coated with an ultra thin poly-electrolyte coating or alternatively with bio-compatible materials. To protect the drugs against photolytic decomposition and oxidation, the drugs and their formulations can be coated with the materials like Titanium dioxide and gelatin respectively. Film coating can be used to protect pharmaceuticals from the effect of moisture. The drugs that are degraded by gastric, intestinal fluids can be stabilized with coating technique by proper deposition of the polymer that are impermeable to biological fluids. Drugs such as Erythromycin, omeprazole that degrade in acidic environment can be protected by enteric coating.