The propagation of intense charged particle beams into vacuum without the aid of externally applied confining magnetic fields is under investigation both theoretically and experimentally. In the configuration under study an intense relativistic electron beam is injected through a localized plasma source into vacuum. Tons drawn into the vacuum region by the electron beam space charge provide the required neutralization for the effective propagation of beam electrons over significant distances. Fxperimental measurements indicate that under optimum conditions, both the ion and electron components of the propagating electron/ion beam are well focused radially. An equilibrium for this propagating electron/ion beam in which both species are in radial force balance has been postulated and matched to both electron and ion beam parameters at the source. Studies of the propagation of such an electron/ion beam across a transverse magnetic field are also reported.