Feynman’s imaginary time path integral formalism of quantum statistical mechanics and the corresponding quantum-classical isomorphism provides a theoretical formalism to incorporate nuclear quantum effects (NQEs) in simulations of condensed matter systems using well-established classical methods such as molecular dynamics (MD) or Monte Carlo (MC). Moreover, path integral methods also have been extended into the dynamical realm to calculate dynamic quantities such as vibrational spectra. Despite the wide success of path integral methods in both statistics and dynamics, they are not without rooms for improvement. These challenges are innate to the classical nature of the ring polymers, or discrete representation of the imaginary time path. In quantum statistics, the path integral methods provide a significant sampling challenge due to the extended phase space of the ring polymers. Moreover in quantum dynamics, the connection between the dynamics of the ring polymer and the real time quantum dynamics remain unclear. To address these distinct challenges, we use ideas from classical statistical mechanics in the context of path integral methods. Coarse-graining of path integral (CG-PI) theory constructs an alternative reductionist representation of the ring polymer using coarse graining, greatly reducing the dimensionality. In this dissertation, the many-body generalization of the one-body CG-PI theory is discussed. Moreover, we also introduce a numerical CG-PI (n-CG-PI) method and modeling scheme that have shown to well capture the structural correlations of realistic molecular systems. In the realm of dynamics, the recently developed generalized Langevin equation analysis of ring polymer molecular dynamics theory (GLE/RPMD) provides an alternative picture of the ring polymer dynamics by directly mapping it into a GLE form. By doing so, we analyze the two different contributions on the dynamics, namely from the system and the bath. The numerical results testify both the importance of the system potential and the higher order interactions of the bath.