The goal of this dissertation is to contribute to the body of scientific knowledge on music interventions for stress reduction. To cope with the negative impact of stress, millions of people around the world use tranquilizing medication, which in turn is associated with numerous contraindications and negative side effects. Therefore, there is an urgent need to develop and examine innovative and non-pharmacological interventions for stress reduction, especially for patient populations known to be more vulnerable to stress such as those with mild intellectual disabilities (MID). Moreover, the stress-reducing qualities of music have been associated with a broad range of positive outcomes in both medical and mental healthcare settings. This dissertation therefore aims to increase scientific knowledge on (a) the effects of different types of music interventions on stress-related outcomes, (b) how and why music interventions may specifically lead to stress-reducing effects, and (c) how stress can be accurately assessed, specifically in people with MID. Overall, this dissertation demonstrates that music interventions in the form of both music listening interventions and in the context of music therapy can greatly benefit patients in medical and mental health care settings. Furthermore, the added value of a qualified music therapist offering the music interventions is emphasized, which can be explained by the personalized, tailored approach of the music therapist. Despite the difficulty of examining these music therapy interventions, more robust research is needed, especially in patient populations proven to be more vulnerable to stress as those with cognitive impairments. Future research that focuses on both efficacy and hypothesized therapeutic factors is crucial to the further implementation of music therapy interventions in healthcare settings, particularly when it comes to stress reduction.