Optical fibers can be heated and stretched down to radii less than an optical wavelength, where much of the optical mode extends into the vacuum. With careful experimental control and understanding of optical modes, we can create ultrathin fibers that guide light adiabatically from a core-cladding guided mode onto a cladding-vacuum mode and back with greater than 99.9% transmission. Using a variety of diagnostic techniques, we can also launch and control higher order modes through such fibers, giving new opportunities for spatially tailoring the evanescent fields. Using an ultrathin fiber we trap atoms in a two-color evanescent field a few hundred nanometers from the fiber surface. Such a system is interesting both as a component of a hybrid quantum system, and as a one-dimensional atomic system with infinite-range interactions.