After a long absence, since 70's, there is a new interest in radiative transfer theory thanks to the work of B. Rutily (Lyon Observatory), with new solutions based on the finite Laplace transform. After a summary of the history of radiative transfer theory, I will indicate why solving the radiative transfer equation brings major difficulties, even for the simplest problem, when the scattering is not neglected. I will introduce the exact method of B. Rutily and the derived code ARTY, which was used to test some numerical methods (e.g. Accelerated Lambda Iteration ALI) and some approximate methods. A few results from these tests will be shown.