The air pollution in large communities has reached a critical state in the last few decades. Transportation, power generation and other civil and industrial activities are responsible of this drastic pollution. The fuel cell technology has come as a new approach to satisfy the ever increasing thirst for power generation and, in the same time, keeping a clean environment. The fuel cell is a direct energy conversion unit from the fuel chemical energy to electrical energy, without conversion first to heat. This paper deal with fuel cell technology, theory of operation, classification and examine its suitability for stationary, mobile and portable power generation units. Comparison between different fuel cell systems is carried out in a systematic way to enable quick search and selection. The paper discusses also the technical limitations to be overcome for the wide application of the fuel cell in transportation and power generation. Application of thermodynamics laws on the fuel cell to analyze its performance has been discussed. The paper concludes that the future of this technology is extremely promising. Therefore, very serious efforts in fuel cell researches are needed to overcome difficulties for commercialization. The fuel cell should be considered as a revolution transforming our science and technology just as that of microprocessor.