Tourism firms operate in a competitive sector where innovating is often a condition for survival. This article presents a theoretical framework for understanding tourist firms’ innovative behaviour and innovation systems in tourism. The innovativeness of tourism firms and its determinants are investigated by analysing quantitative as well as qualitative data comparing Spain and Denmark. A taxonomy of tourism firms is suggested and the firms’ characteristics which influence their innovativeness are presented. Additionally, the role of innovation networks is discussed, as is the role of innovation systems. The article suggests that large size, professionalism, but also entrepreneurship among small tourism firms are important determinants of innovation. Varied innovation networks are another determinant as are supportive innovation systems. These determinants favour Spanish firms, which are more innovative than Danish ones. In the final section, policy recommendations are presented.