Spectral methods are global methods, where the computation at any given point depends not only on information at neighboring points, but on information from the entire domain cite{d}.
Spectral methods, in the context of numerical schemes for differential equations,
belong to the family of weighted residual methods (WRM). WRM represents
a particular group of approximation techniques, in which the residuals
are minimized in a certain way and there by leading to specific methods including
Galerkin and collocation formulations cite{e}.
The objective of this chapter is to formulate spectral methods in a
general way by using the notion of residual. Several important tools, such as discrete transform and spectral differentiation, will be introduced. These are basic ingredients for developing efficient spectral algorithms.