A nonperturbing probe that utilizes a focused ion beam has been developed to measure the position and profile of a tightly bunched charged particle beam (CPB). The ions are injected across the path of the CPB and are deflected by the electromagnetic field of the CPB. Deflected ions are detected by a gated microchannel plate detector and video camera. From the magnitude of the deflections, one can determine the position, radial profile, and in some cases, the axial length of the CPB. Ion parameters can be adjusted to tailor the probe to a wide range of CPB parameters, from submicron, ps bunches to millimeter-sized, quasicontinuous beams. We present the theory of operation of the probe, provide a number of numerical examples to illustrate its capabilities, and describe a proof-of-principle version of the probe that we built and successfully tested at SLAC. The experimental results obtained with this prototype version have shown the ion probe diagnostic to be feasible, reliable, and well understood by the theory and models. ©1997 American Institute of Physics.