Since the advent of scanning probe microscopy (SPM) over a quarter of a century ago, several scientific fields, including materials science, have been transformed. Initial work with the scanning tunneling microscope (STM), whereby real-space imaging at the atomic scale was used to verify the hitherto predicted 7×7 reconstruction of the Si(111) surface, immediately catapulted the STM into mainstream science. So much so, that it led to the award of the Nobel Prize in 1986 to G. Binnig and H. Rohrer for their invention of the STM, along with the pioneer of electron microscopy, E. Ruska. Since those early days, aided by the development of the atomic force microscope (AFM) a few years after the STM, we have learned much about the structure and function of matter at the nanometer scale and below. As the operation of the STM itself is dependent on quantum mechanics, it has proven to be invaluable for fundamental research into surface and electron physics. Initial work involved probing the nature of the tunnel barrier between the STM tip and a metal or semiconductor surface, and was quickly followed by investigations of the surfaces themselves, culminating in the now well-known beautiful visualizations of electron standing waves in Eigler's ‘quantum corral’ structures