This research analyses the presence of tourism innovation, as a transformation process in spa tourism in Spain. The methodological sequence is: 1) Identification of studies through databases and registers, 2) Analysis of innovation in thermal tourism in Spain, 3) Identification of innovation groups and variables of interest for thermal tourism. Different methods and techniques are used, such as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, the Free Word Cloud Generator and the analysis of clusters and concurrences through VOSViewer. The results show the need for a continuous innovation process, since it is used as a temporary stabilizer and not as a source of continuous improvement. The contributions, limitations, and variables on tourism innovation in spa tourism in Spain are identified. In addition, 5 dimensions on how understanding innovation in spa tourism are identified (client profile and satisfaction, innovation objectives, innovation capacities, new or improved products and services, and territorial development). In addition, 30 variables associated with these dimensions are identified, describing the current and future management of innovation in Spanish thermal tourism. As far as we know, this study is the first review on tourism innovation in spa tourism in Spain, establishing a theoretical basis for future studies.