In this book are presented the theory and methods for solving nonlinear synthesis problems of various types of radiating systems arising during optimal design. Variational formulations of problems, in which are given only requirements to amplitude directivity pattern (DP) or DP by power, and to amplitude and phase (amplitude or phase) of distribution of excitation sources of electromagnetic fields, are given. Characteristic feature of these classes of problems is nonuniqueness and branching (or bifurcation) of existing solutions. Research and finding of optimal solutions of the synthesis problems is reduced to the study and numerical solution of nonlinear integral equations of Hammerstein type. There are given the numerical methods to solving the synthesis problems of such radiating systems: linear antennas, antenna with flat aperture, linear and planar antenna arrays (AA), microstrip arrays, adaptive AA, hybrid reflector and lens antennas and synthesis on the basis of contour DPs of fixed and variable form. This book can be used by the experts in the antennas theory, applied mathematics and mathematical physics, by students and post-graduate students of corresponding specialties.