The Ph.D. is the highest degree awarded to a scholar after he or she has specialized in a subject. The degree is awarded after a certain amount of original research in that subject is documented by producing a dissertation or thesis, often of sizeable length. The degree is often a prerequisite for permanent employment as a university lecturer or as a researcher in some sciences, though this varies. In some fields, such as engineering, a doctoral degree may be considered desirable but not essential for employment.