Purpose of review Mesenchymal stem or stromal cells (MSCs) are multipotent cells with immunomodulatory and regenerative capacities. These properties make MSCs interesting for use as a cell therapeutic agent in solid-organ transplantation (SOT). Their applicability in SOT has recently been evaluated in numerous preclinical and clinical studies, which are reviewed in this article. Recent findings Animal transplant studies indicate that MSCs can improve the outcome of SOT. In-vitro research has resulted in new insights into the paracrine mechanism and cell-dependent mechanism of action, migratory behaviour and immunogenicity of MSCs that are relevant for application of MSCs in SOT. Currently, six trials are registered to evaluate MSCs in phase I/II studies in SOT. The first clinical data are now published describing MSC infusion in organ transplant recipients. Summary The research to date confirms that MSCs are a promising cell therapeutic agent for application in SOT and the first clinical trials have been initiated. The exact mechanisms of MSC therapy have, however, not been elucidated. Further basic and clinical research is needed to develop effective MSC therapy in SOT patients.