We report a comprehensive study on the molecular structure and dynamics of large polyethylene-oxide (PEO) rings in the melt and in symmetric ring/linear blends. The investigation of the ring conformation were performed by Small Angle Neutron Scattering (SANS): For all rings we observed a cross over from a compact structure at large distances to Gaussian conformations at shorter distances. The cross over occurs at a distance along the ring of N_e,0=45±2.5 monomers providing evidence for the theoretically predicted elementary loops that build the ring conformation. The radius of gyration  R_g(N)  follows the result of numerous simulations. However, other than claimed the cross over to mass fractal behavior is not reached. The self-similar ring dynamics was accessed by PFG-NMR and neutron spin echo (NSE) spectroscopy: We find center of mass diffusion taking place in three dynamic regimes starting (i) with a strongly sub-diffusive domain  (ii) a second sub-diffusive region   that (iii) finally crosses over to Brownian diffusion. While the exponent 0.75 was predicted by theory, we attribute the first to the effect of cooperative dynamics resulting from the correlation hole potential. The internal dynamics at scales below the elementary loop size is well described by ring Rouse motion. At larger scales the dynamics is self-similar and follows very well the predictions of the scaling models with preference for the self-consistent fractal loopy globule (FLG) model. Ring/linear blends were studied over the full concentration range. Both the blend viscosity as well as the microscopic dynamics were studied. Applying neutron spin echo (NSE) spectroscopy on samples containing a fraction of labelled rings, we essentially observed the internal ring dynamics and its modifications as function of ring volume fraction φ_R. We observe an increased enslavement of the ring dynamics with higher linear volume fraction. The increasing ring enslavement well correlates with the relative increase of the blend viscosity.  At a ring volume fraction φ_R = 0.5 where the viscosity increase attains its maximum, the spectral shapes are still local reptation type, however the entanglement network is diluted.