This chapter describes the various forces that exist between the tip and sample during AFM operation. Included in this chapter is a description of van der Waals forces, Keesom forces, Debye forces, repulsive forces, and capillary forces. An algebra-based description of these tip-sample forces is also included in this chapter. In this chapter, readers will also find a graphical analysis of tip-sample forces involving force curves. Readers will know how to interpret force curves after reading this chapter. Lastly, this chapter includes a laboratory investigation involving a force curve analysis of polymer and metallic nanogrids.