Atomic force microscopy (AFM) is the most valuable scanning probe technique, which is based on high-resolution imaging of surfaces with a sharp probe. In main function, AFM is used for quantitative studies of surface roughness, a precise profiling of complex surface patterns and visualization of surface structures as small as individual atoms and molecules. AFM studies are performed at various temperatures and environment (air, vacuum, under liquid). Different phenomena such as thermal transitions, selective swelling, component diffusion, phase separation, etc. can be monitored in real space and in real time. In addition to surface imaging, AFM is used for sub-micron studies of mechanical properties. Reliability and reproducibility of such testing will be analyzed in relation to tip geometry, cantilever stiffness and data analysis of force curves and indent profiles. Examples are taken from studies of thin films and examination of mechanical behavior in wide frequency range (0.1 Hz – 100 kHz).