Abstract: It is well known that atomically well resolved images of a solid surface canbe routinely obtained with the field ion microscope (FIM), and their chemicalspecies identified in the time-of-flight atom probe. These instruments have beenwidely used in studying the behavior of single atoms on solid surfaces, and inmeasuring the absolute composition of surfacc layers. The range of materialsaccessible to FIM and atom-probe studies include most metals, ranging form Beto U, semiconductors, and some ionic compounds also. Surface diffusion parame-ters of single atoms, interaction energies between adsorbed atoms and between anadsorbed atom and substitutional impurity atoms, the polarizability and surfaceinduced dipole moment and other properties of single atoms ou solid surfaces cannow be obtained with the FIM. The absolute composition of surface atomic layerscan be analyzed one by one in the atom-probe. Preliminary results have beenobtained for the early stages of silicide formation on metal surfaces. Recently aconsiderable progress has been made in studying the gas-surface interactions, andadsorption and desorption of gases using the newly developed pulsed-laser atom-probe. Here we briefly describe the principles and designs of the FIM and theatom-probe. We also discuss the principles and results of some quantitative FIMsingle atom experiments.