Driving under the influence of fatigue and drowsiness is one of the leading causes of accidents throughout the world. The United States Department of Transportation (USDOT) estimates that every year driver fatigue causes close to 100,000 crashes in the United States. These accidents results in1,544 fatalities, 71,000 injuries, and $12.5 billion in monetary losses in the US alone. Around the world, thousands of lives are lost each day due to road accidents. The National Road Safety Secretariat (NRSS) Pakistan estimates, the annual economic cost of highway crashes over rupees one hundred billion (over US$ 1.6 billion) for Pakistan. This paper provides a comprehensive review of the previous literature regarding driver fatigue and drowsiness research, the present state of research and the future trends. Various factors that may contribute to driver fatigue and drowsiness, Fatigue related countermeasures from various sources along with their merits are discussed. The Center for Intelligent Systems Research (CISR) of the George Washington University conducted an experiment at their Vehicle Simulator Laboratory to study driver drowsiness. Results of this study and description of the algorithm are provided. A comprehensive list of references is provided at the end.