The vibrational dynamics of formic acid monomer (FAM) and dimer (FAD) is investigated from machine-learned potential energy surfaces at the MP2 (PES MP2 ) and transfer-learned (PES TL ) to the CCSD(T) levels of theory. The normal modes and anharmonic frequencies of all modes below 2000 cm −1 agree favourably with experiment whereas the OH-stretch mode is challenging for FAM and FAD from normal mode analyses and finite-temperature MD simulations. VPT2 calculations on PES TL for FAM reproduce the experimental OH frequency to within 22 cm −1 . For FAD the VPT2 calculations find the high-frequency OH stretch at 3011 cm −1 , compared with an experimentally reported, broad (∼ 100 cm −1 ) absorption band with center frequency estimated at ∼ 3050 cm −1 . In agreement with earlier reports, MD simulations at higher temperature shift the position of the OH-stretch in FAM to the red, consistent with improved sampling of the anharmonic regions of the PES. However, for FAD the OH-stretch shifts to the blue and for temperatures higher than 1000 K the dimer partly or fully dissociates using PES TL . Including zero-point energy corrections from diffusion Monte Carlo simulations for FAM and FAD and corrections due to basis set superposition and completeness errors yield a dissociation energy of D 0 = −14.23±0.08 kcal/mol compared with an experimentally determined value of −14.22±0.12 kcal/mol.