Background: In the Netherlands, the spiritual dimension in healthcare became marginal in the second part of the twentieth century. In the Dutch healthcare sys- tem, palliative care is not a medical specialization and teaching hospitals do not have specialist palliative care units with specialized palliative care teams. Palliative care in these hospitals is delivered by healthcare professionals in general depart- ments (mainly curative focused ones), and is based on multidisciplinary guide- lines supported by palliative care consultation teams. A national multidisciplinary guideline on spiritual care is included, but standardized training based on this guideline still lacks. Implementation of this guideline is expected to have a posi- tive effect on quality of care but is in an early state, the role of the specialists in this field—the healthcare chaplains—is developing. The objective of this article is to present the protocol of this study and stimulate discussion about methods of research on spirituality and spiritual care. Methods and Findings: This action research study is planned as an explorative mul- ticentre trial. Healthcare chaplains of ten teaching hospitals will offer training on spiritual care in palliative care for healthcare professionals. What is the effect of this intervention on the competences of clinical teams? What is the effect on the perceived care and treatment as experienced by patients? The effects of the intervention on the competences of the clinicians will be meas- ured once pre-study and twice post-study. Effects on patients’ physical symptoms and spiritual distress, and the perceived focus of caregivers on their spiritual needs or existential questions will also be measured pre- and post-study.