The multi-configuration time-dependent Hartree (MCTDH) approach is a powerful tool for studying quantum dynamics, as well as for determining the vibrational states (energies and wavefunctions) of molecules/molecular complexes. However, the efficient use of MCTDH requires the potential energy surface (PES) and kinetic energy operator (KEO) to be represented in sum-of-product (SOP) form. In this talk, I will introduce MCTDH, the reasons for the need for SOP form, and approaches our group has used to fit SOP PESs based upon ab initio data [1-5]. A brief introduction will be given to one approach we have applied for generating SOP PESs using a single layer neural network with exponential activation functions (so-called expNN). We have successfully applied this methodology to developing accurate SOP PESs for HFCO and HONO [1-4]. More recently, we have developed a semi-automatic adaptive sampling and fitting procedure for generating SOP PESs based on a high-dimensional model representation is presented [5]. The adaptive sampling procedure and subsequent fitting relies on energies only and can be used for re-fitting existing analytic potential energy surfaces in SOP form or for direct fits from ab initio computations. The method is tested by fitting ground electronic state potential energy surfaces for small to medium sized semi-rigid molecules, i.e., HFCO, HONO, and HCOOH, based upon ab initio computations at the CCSD(T)-F12/cc-pVTZ-F12 or MP2/aug-cc-pVTZ levels of theory. Vibrational eigenstates are computed using block improved relaxation in the Heidelberg MCTDH package and compared to available experimental and theoretical data. The new potential energy surfaces are compared to the best ones currently available for these molecules (including those from expNN) in terms of accuracy, including of resulting vibrational states, required numbers of sampling points, and number of fitting parameters. The present adaptive procedure leads to compact expansions and scales well with the number of dimensions for simple potentials such as single or double wells. [1] E. Pradhan and A. Brown, J. Chem. Phys. 144, 174305 (2016). [2] E. Pradhan and A. Brown, J. Mol. Spectrosc. 330, 158-164 (2016). [3] E. Pradhan and A. Brown, Mol. Phys. 118, 12 (2020). [4] E. Pradhan and A. Brown, Phys.Chem.Chem.Phys., 19, 22272 (2017). [5] A. Aerts, M.R. Schäfer, and A. Brown, J. Chem. Phys. 156, 164106 (2022).