Dysfunction of tear film or dry eye disease (DED) is a multifactorial and common disease that results in symptoms of discomfort and visual disturbance with potential damage to the ocular surface. It is characterized by a loss of homeostasis of the tear film, in which tear film instability and hyperosmolarity play etiological roles. DED still poses a diagnostic dilemma to clinicians, particularly due to its various and multiple causative factors. The ill effect of the disease’s complexity is that there is presently no test or set of tests which could be considered a “gold standard” for its diagnosis and monitoring the course of the disease. Regardless of many tests being indicators of DED, their value and the interpretation of the results have been widely debated. Current methods of diagnosis include a slit-lamp examination with and without different stains, assessment of tear break-up time, clinical examination for lid margin disease, tear meniscus assessment, tear osmolarity assessment and Schirmer test. Without a diagnostic standard of disease management, often DED testing and treatment are not performed until a patient is symptomatic and seeks help. Because of all this, DED is becoming a growing public health concern as it can significantly impact a person’s vision and lead to a diminished quality of life. This graduate thesis discusses the classification and diagnostic approaches of DED.