The transport approach is a useful tool to study dynamics of non-equilibrium systems. For heavy-ion collisions at intermediate energies, where both the smooth nucleon potential and the hard-core nucleon-nucleon collision are important, the dynamics are properly described by two families of transport models, i.e., the Boltzmann-Uehling-Uhlenbeck approach and the quantum molecular dynamics approach. These transport models have been extensively used to extract valuable information of the nuclear equation of state, the nuclear symmetry energy, and microscopic nuclear interactions from intermediate-energy heavy-ion collision experiments. On the other hand, there do exist deviations on the predications and conclusions from different transport models. Efforts on the transport code evaluation project are devoted in order to understand the model dependence of transport simulations and well control the main ingredients, such as the initialization, the mean-field potential, the nucleon-nucleon collision, etc. A new era of accurately extracting nuclear interactions from transport model studies is foreseen. 2 from 50 MeV to 2 GeV, where the nucleon degree of freedom dominates the dynamics, and both the smooth nuclear potential and the hard-core nucleon-nucleon collisions become important. The central purpose of intermediate-energy heavy-ion collisions is to extract the equation of state (EOS) of the hot and dense nuclear matter formed during the collisions, while the uncertainties mostly come from the isospin-dependent part, i.e., the nuclear symmetry energy.In order to describe properly the dynamics of intermediate-energy heavy-ion collisions, transport approaches at this energy regime are mostly developed along two directions: the Boltzmann-Uehling-Uhlenbeck (BUU) approach and quantum molecular dynamics (QMD) approach. The BUU approach basically models the time evolution of the one-body phase-space distribution based on the BUU equation numerically using the test-particle method, and the QMD approach models the time evolution of nucleons under a many-body Hamiltonian with the wave function of each nucleon represented by a Gaussian wave packet. Both approaches can be derived from many-body theories with various approximations. Without nucleon-nucleon collisions, the BUU approach reduces to the Vlasov approach, which is similar to the TDHF approach. On the other hand, it is difficult to solve exactly the extended TDHF approach, which incorporates the collision contribution into the TDHF approach [3]. Both the BUU approach and the QMD approach include mainly three ingredients: the initialization of projectile and target nuclei, the mean-field potential for each nucleon, and the nucleon-nucleon collision in the dynamical evolution. The mean-field potential can be obtained from effective in-medium nucleon-nucleon interactions based on the Hartree or Hartree-Fock method, and in this way the microscopic nuclear interaction is related to the macroscopic nuclear EOS through the energy-density functional form.So far both the BUU appr...