Near-field optics is based on the interaction of an electromagnetic field with nanostructures in all its applications. To understand the properties of nearfield optics devices, the electric field in the near-field region and its interaction with the object have to be calculated. This problem is particularly difficult due to the low symmetry of the near-field geometry and the small size of the system compared to the wavelength. The geometrical optics or the scalar physical optics approximations are no longer valid. Moreover, the near-field light, after interacting with the sample, will be diffracted and converted into far-field light; therefore the calculation becomes more complicated. Near-field simulation means to calculate numerical solutions of Maxwell equations.