Atomic Force Microscopy (AFM) is a powerful tool for studying surface morphology of materials at the nano scale. In addition, various advanced properties such as frictional, mechanical, and electrical can be also obtained using the AFM. In this study, we discuss about principles of basic AFM modes such as contact, non-contact, and tapping mode. Starting from the fundamental theories of atomic interactions which typically used for AFM measurements, to main hardware components of the AFM. In addition, crucial points (e.g., set point, feedback) of each mode are mentioned and discussed. In contact mode, the tip physically contacts the sample with a given force set point. This set point is maintained constant during scanning. The principle is relatively simple among three modes. However, damages to tip and sample are readily occur due to contact sliding. In contrast, non-contact mode allows topography measurement without contacting the surface. Therefore, tip and sample can be preserved. Tapping mode (i.e., intermittent contact mode) shares similar principle with non-contact mode. Nonetheless, the tip taps the surface during scanning to measure additional information on material properties distribution (e.g., modulus distribution). The target of this session is to help understand the interactions between tip and sample based on fundamental knowledge on principles of AFM. After all, some images which measured with above three modes are represented.