The Ne-NH3 van der Waals complex was investigated through analysis of microwave spectra and the construction of ab initio potential energy surfaces. Rotational spectra of the ground internal rotor state of Ne-NH3 were recorded between 7 and 24 GHz using a Balle-Flygare-type Fourier transform microwave spectrometer. In total, ten isotopomers were studied, which include Ne-20 and Ne-22 paired with NH3, (NH3)-N-15,-ND3, ND2H, and NDH2. The spectroscopic constants including the N-14 quadrupole coupling constants were determined and used to estimate structural and dynamical details of the van der Waals complex. For each deuterium-substituted isotopomer, a tunneling splitting was observed due to the inversion of NH3 within the ground state of the complex. One of these inversion components is missing for the NH3 and 15NH(3) containing isotopomers for spin statistical reasons. Ab initio potential energy surfaces were constructed for three different umbrella angles of NH3 within the complex to provide information about the interaction along the NH3 inversion pathway. The interaction energies were calculated using Moller-Plesset perturbation theory to fourth order. All three surfaces have minima corresponding to structures where the van der Waals bond (the line from the center of mass of NH3 to the Ne atom) lies perpendicular to the C-3 axis of NH3, with the neon atom sitting between two hydrogen atoms. At this orientation, the potential well depth is 62.66 cm(-1) (285.5 mu hartree) at a van der Waals bond length of 3.30 Angstrom (6.24 bohr) for the experimental equilibrium NH3 monomer geometry.