Abstract: The development of microscopes makes it possible to observe the physical world at the micro- and nano-scales. The invention of the atomic force microscope (AFM) enables us to directly contact the microscopic world and measure the interactions. With the help of this micro- and nano-scale hand, the AFM technique, is increasingly used for exploring and understanding the physical world and even the living world at micro- and nano-scales. This paper reviews the development of the microscope, the working principle of the AFM and its application in studying cell mechanics.