A key component in understanding the L-H transition is the behaviour and interactions of Zonal Flows (ZF), Geodesic Acoustic Modes(GAM) and Drift-Waves. To that end, this thesis explores the behaviour of GAMs and the interactions between ZF and drift-waves. For investigating the ZFs and drift-wave interaction, a new spatial averaging technique is developed and applied to the linearization of the modi_ed Hasegawa-Wakatani model. A global dispersion relation for drift-waves in the presence of zonal ows is obtained [9]. Subsequently both the linear and non-linear behaviour of GAMs is investigated by analysing data from a uid simulation of the MAST(Mega Ampere Spherical Tokamak) tokamak. Evidence of linear physics is obtained by investigating the spatial and temporal modal structures of GAMs using continuous wavelet transforms and fast fourier transforms. Non-linear physics is investigated using bicoherence analysis and it is shown that non-linear coupling exists between GAM and low frequency modes. Additionally self-interaction of GAMs is also observed and a poloidal dependence of this behaviour was recovered.