In this book, we introduced the concept of Internal transport barrier (ITB) which is generally indulged to grow up the regions of reduced transport which can be helpful for tokomak operation. Internal transport barriers are created near the low order rational surface. i.e. (q = 2, 5/2 and 3). These ITBs are reactive to some conditions with regards to MHD instabilities, which generate a considerable plasma flow, creating magnetic islands, which are wished as probable mechanisms for the development of ITB. Double tearing modes become active due to electron viscosity and the MHD flows in the development the modes is extended from quasi-linear solution in a slab geometry to nonlinear solution in cylindrical geometry for the torus of large aspect ratio. The DTM mediated by electron viscosity is considered to trigger an ITB with non-monotonic q- profiles in advance tokomak (AT) operation.