The principles on how the AFM works are very simple. A microfabricated cantilever with a sharp tip is deflected by features on a sample surface, much like in a phonograph but on a much smaller scale. The atomically sharp tip is scanned over a surface with feedback mechanisms that enable the piezo-electric scanners to maintain the tip at a constant force (to obtain height information), or height (to obtain force information) above the sample surface. The force between the tip and the sample surface is very small, usually less than 10-9 N. The detection system does not measure force directly. It senses the deflection of the micro cantilever. The detecting systems for monitoring the deflection fall into several categories. The first device introduced by Binnig was a tunneling tip placed above the metallized surface of the cantilever. This is a sensitive system where a change in spacing of 1 Å between tip and cantilever changes the tunneling current by an order of magnitude. It is straightforward to measure deflections smaller than 0.01 Å by the optical techniques. The interferometer is the most sensitive of the optical methods, but it is somewhat more complicated than the beam-bounce method which was introduced by Meyer and Amer. The beam-bounce method is now widely used as a result of the excellent work by Alexander and colleagues. In this system an optical beam is reflected from the mirrored surface on the back side of the cantilever onto a position-sensitive photo detector. In this arrangement a small deflection of the cantilever will tilt the reflected beam and change the position of beam on the photo detector allowing the deflection to be measured and assembled into an image of the surface. A third optical system introduced by Sarid uses the cantilever as one of the mirrors in the cavity of a diode laser. Motion of the cantilever has a strong effect on the laser output, and this is exploited as a motion detector. According to the interaction of the tip and the sample surface, the AFM can be classified as repulsive or Contact mode and attractive or Noncontact mode. Now the Tapping mode shows a prosperous future to image the micro-world.