The conjunctiva is a soft, smooth and transparent membrane located on the inner surface of the eyelid and the surface of the eye. Conjunctivitis is the “inflammation” of the conjunctiva. It is a common and frequent clinical condition. The causes of conjunctivitis can be divided into two categories, infectious and non-infectious, depending on their different properties. 1. Infectious: Inflammation of the conjunctiva due to infection by pathogenic microorganisms. Non-infectious: Allergic inflammation caused by local or systemic allergic reactions is the most common, and external physical and chemical factors such as light and various chemicals can also be causative factors. Clinical symptoms are: red and itchy eyes, foreign body sensation, burning sensation, heavy eyelids, increased secretions, photophobia, lacrimation and varying degrees of vision loss when the lesion involves the cornea. Treatment should be based on the specific etiology. In case of infectious conjunctivitis: antibacterial or antiviral eye drops or eye ointment. Depending on the etiologic diagnosis, the appropriate therapeutic medication is selected. For example, tobramycin eye solution and erythromycin eye ointment are available for bacterial infections, and acyclovir eye solution is available for viral infections. In case of non-infectious conjunctivitis, such as allergic conjunctivitis, do not abuse antibiotics, but use anti-allergic eye drops, such as sodium cromoglycate ophthalmic solution. Conjunctivitis is a common and frequent clinical disease.