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Although the incidence of prostate cancer is high, improvements in treatments have led to high survival rates in patients with low- and intermediate-risk prostate cancer. Therefore, it is even more important that treatments for these patients are minimally invasive and cause as little side effects as possible. The last decades, radiotherapy treatments have changed significantly. One of the clinically introduced innovations is the MR-Linac, a combination of a linear accelerator and an MRI scanner. This machine allows high-quality imaging before and during treatment and daily treatment plan optimisation based on the changing anatomy. This enables more precise radiotherapy and therefore better sparing of healthy organs, which will potentially lead to less side effects such as urinary complaints and erectile dysfunction. This thesis provides insight into the clinical introduction and first period of prostate cancer treatment on the MR-Linac. In part 1 of this thesis, new workflows and technological developments for MRI-guided prostate cancer treatment are presented, which are aimed at enabling extremely hypofractionated radiotherapy for prostate cancer in one or two treatment fractions. With these new workflows, the irradiated volumes can be reduced significantly. Furthermore, early (patient-reported) outcomes of MRI-guided prostate cancer radiotherapy are investigated within two cohort studies, including the international MOMENTUM study. These clinical results are already promising. Part 2 of this thesis focusses on re-irradiation in patients with recurrent prostate cancer after primary radiotherapy treatment. We present research on the feasibility of so-called single-fraction ‘focal salvage’ radiotherapy using external beam radiotherapy on the MR-Linac. The work presented in this thesis is part of the first steps towards MRI-guided, extremely high-precision radiotherapy treatment for (recurrent) prostate cancer in only one or two treatment sessions.