This book provides study on reliability properties of residual life time and inactivity time, series and parallel system and decision making in intuitionistic fuzzy environment. Decision making generally depends on two factors - the amount of information associated with an alternative and the reliability of information. The theory of intuitionistic fuzzy set is well suited while dealing with imprecise or uncertain decision information, image edge detection, medical diagnosis, pattern recognition, human expressions like perception, knowledge and behaviour, by reflecting and modelling the hesitancy present in real life situations and decision making.