The cornea is the clear window at the anterior surface of the eye. Corneal clarity is essential for vision. Corneal transplantation can restore sight when the cornea is diseased, and the cornea is the most commonly transplanted solid tissue. In penetrating corneal transplantation (penetrating keratoplasty), the whole thickness of the cornea is replaced. New surgical techniques of lamellar keratoplasty have been developed in which only the diseased layers of the cornea are replaced, to minimise the risks of graft rejection and optical distortion. Both penetrating and lamellar grafts may fail and need to be replaced. An implication for histopathologists is that the specimen sent for pathological analysis from a patient with a failed lamellar graft will differ from that from a patient with a failed penetrating graft.