The paper deals with the Freak Wave with its mathematical basis. First, the concept of Freak Waves in the actual ocean is described from the beginning of their research up to present state of the arts. Non-linear wave theory in particular NLS equation is briefly explained with its important solutions including envelope soliton and the breather (SFB). The latter solution is surmised to be a possible mechanism of the occurrence of Freak Waves. It-rises from ordinary wave train caused by modulational instability well known after Benjamin-Feir. I deduced this most representative example within the technique of elementary mathematics herein, however most powerful and complex method of Inverse Scattering Technique (IST) revealed the decomposition of Freak Waves from ordinary quasi linear waves by Osborne et al.. For the practical application of the theory in the field of ocean engineering and naval architecture, the in-situ data acquisition and/or real time observation in the open ocean are indispensable to evade from this tremendous disaster. A crucial problem remains in this research is mentioned with the proposals in future.