Since its invention, the Atomic Force Microscope has emerged into one of the most useful tools in nanotechnology due to its acclaimed abilities in exploring surface topography, micro- and nanoscale manipulation and characterization. The nonlinear interaction between the cantilever tip and the sample surface has been studied in great detail and a thorough understanding of the cantilever dynamics can improve measurements and lead to new methods for identification, manipulation and characterization. One of the biggest challenges in the field of AFM is related to the identification of the cantilever tip size. The accuracy of measurements in AFM is directly related to the size and geometry of this tip. It is desired that the tip condition can be continuously monitored in between or even throughout measurements in order to provide high quality measurements. In this thesis project, a methodology for tip assessment is introduced based on the nonlinear dynamic response of the cantilever. The method consists of the acquisition of frequency response curves in the attractive regime where the influence of the tip radius is predominant. Experimental frequency response curves are fitted to the tip-sample interaction model that includes the van der Waals forces. It is found that exploiting the nonlinear dynamic response of the cantilever is a safe and accurate method for tip assessment.