Focusing of Singular beam has attracted great deal of attention in recent years due to various practical applications and in physical optics. Importance has also been realized in polarization and pupil function engineering for desired focused structure. Quality of the focusing system plays a very important role in shaping the focused structure, and any imperfection in focusing system results in deformation or an increase in the size of the focal spot. This book reports detail investigations on the focusing of singular beams by high and low numerical aperture systems. Impact of aberrations on the focused structure is also discussed in the context of STED microscopy.