We present three-dimensional simulations of transport and field-emission properties of multiwall carbon nanotubes. The structure considered for the transport properties is the (5,5)@(10,10)@(15,15)@(20,20) multiwall nanotube. When electrons are injected into the inner (5,5) or outer (20,20) layer of this structure, it is observed that around 70% of the current keeps propagating in the shell it is injected into and that the fraction of the current that reaches the opposite shell is of a few percents at most, even after propagation over micron-long distances. For the simulations of field emission, the (5,5)@(10,10)@(15,15) structure is considered. For an extraction field of 2.5 V/nm, the emission obtained with a convex termination is around eight times larger than that obtained with a flat one. The emission from these convex and flat-terminated structures is, respectively, 35 and 21 times smaller than the total current obtained by considering the single-wall components separately. (C) 2003 American Vacuum Society.