The tomographic atom probe (TAP) is the most advanced of the three-dim
ensional atom probes currently in use. Atom probes are unique in that
both the lateral and the depth resolution are high. The general develo
pment of atom probes and the principle of operation of the TAP, in whi
ch the sample is field evaporated atomic layer by atomic layer, are ou
tlined. The analysis of a nickel base superalloy is given as an exampl
e of an application in metallurgy.