Keratoconus (KC) is a progressive non-inflammatory ectatic corneal disease typified by corneal thinning and conical protrusion, as well as irregular astigmatism with a varying-degree visual impairment. A literature review on the disease epidemiology, classification and diagnosis is presented. Current clinical practice most commonly relies on the Krumeich’s adaptation of ABCD grading system by M. Belin and M. Amsler. The KC diagnosis requires a comprehensive approach that integrates a variety of methods. Scheimpflug imaging with the corneal biochemistry assessment is performed with a Pentacam Oculus keratotomograph in combination with a Corvis ST device. The result is expressed as diagnostic indices, CBI (Corvis Biomechanical Index), BAD-D (Belin/Ambrósio Enhanced Ectasia Index total deviation) and TBI (Tomographic Biomechanical Index). The use of optical coherence tomography is necessary to perform corneal epithelial thickness mapping as well as pachymetry to rule out hidden stromal thinning.