Preface.- The Newton-Kantorovich theorem.- Operators with Lipschitz continuous first derivative.- Operators with Hölder continuous first derivative.- Operators with Hölder-type continuous first derivative.- Operators with w-Lipschitz continuous first derivative.- Improving the domain of starting points based on center conditions for the first derivative.- Operators with center w-Lipschitz continuous first derivative.- Using center w-Lipschitz conditions for the first derivative at auxiliary points.