The general concept for the solution of operator equations described in Chapter 2 relies to a great extent on the availability of appropriate wavelet bases. During the past years, much effort has been invested in constructing various types of wavelets, including biorthogonal ones which are well suited for the numerical analysis of operator equations of the form (2.11). When speaking about ‘wavelets’, here always a pair of biorthogonal wavelets Ψ, Ψ is meant, satisfying the Riesz bases, the locality and the duality properties (2.17), (2.18), (2.19), (2.22) and (2.24).