The main factors determining the accuracy of computed rate constants are the reaction energies and the energy barriers for all the elementary steps involved in the reaction under investigation. In the absence of species with strong multi-reference character and/or non-adiabatic effects, the coupled cluster (CC) approach delivers accurate results provided that the most important classes of excitations are included together with complete basis set (CBS) extrapolation, core-valence (CV) correlation and, if needed, other minor effects (scalar relativistic, diagonal non-Born-Oppenheimer, spin-orbit). Due to an effective error compensation single, double, and (perturbative estimates of) triple excitations are usually sufficient, leading to the CCSD(T)-CBS+CV model, which is often considered the gold standard of contemporary computational chemistry. Next, zero point energies (ZPEs) and finite temperature contributions (FTCs) come into play, which are determined by geometries and vibrational frequencies. In this connection, effective approaches going beyond the standard rigid rotor/harmonic oscillator (RRHO) model are needed especially when light atoms or hindered rotors are involved. Finally, barrierless entrance or exit channels are often encountered for reactions in the gas-phase, which require the accurate description of non-covalent interactions.