Vacuum structure in QCD and Correlation functions

We discuss here a model of QCD vacuum in terms of quark antiquark and gluon condensates alongwith their fluctuations. The correlation functions of hadronic currents in such a vacuum are evaluated to extract hadron properties. The presence of fluctuations of the condensates are emphasized. The structure of vacuum is then generalised to finite temperatures to study correlation functions at finite temperatures. Finally, we discuss the vacuum structure at finite densities with diquark condensates in a Nambu JonaLasinio type model. The coupled mass gap and superconducting gap equations are solved selfconsistently. For certain parameters of the model nontrivial solutions of both the gap equations are obtained. The equation of state is also computed.