This book presents Complex Harmonic Splines (CHS), which gives an approximation to the Complex Harmonic Function (CHF), in particular the conformal mapping with high accuracy from the unit disc to a domain with arbitrary shape. The volume develops various periodic quasi-wavelets which can be used to solve the Helmholtz integral equation under some boundary conditions with complexity O(N). The last part of the work introduces a class of periodic wavelets with various properties. Audience: This volume will be of interest to applied mathematicians, physicists and engineers whose work involves approximations and expansions, integral equations, functions of a complex variable and numerical analysis.