Purpose. When introducing innovations to health care, it is important to gain insight into determinants that may facilitate or impede the introduction, in order to design an appropriate strategy for introducing the innovation. To obtain an overview of determinants of innovations in health care organizations, we carried out a literature review and a Delphi study. The Delphi study was intended to achieve consensus among a group of implementation experts on determinants identified from the literature review. Data sources. We searched 11 databases for articles published between 1990 and 2000. The keywords varied according to the specific database. We also searched for free text. Forty-four implementation experts (implementation researchers, programme managers, and implementation consultants/advisors) participated in the Delphi study. Study selection. The following studies were selected: (i) studies describing innovation processes, and determinants thereof, in health care organizations; (ii) studies where the aim of the innovations was to change the behaviour of health professionals; (iii) studies where the health care organizations provided direct patient care; and (iv) studies where only empirical studies were included. Data extraction. Two researchers independently selected the abstracts and analysed the articles. The determinants were divided into four categories: characteristics of the environment, characteristics of the organization, characteristics of the user (health professional), and characteristics of the innovation. When analysing the determinants, a distinction was made between systematically designed and non-systematically designed studies. In a systematic study, a determinant analysis was performed and the innovation strategy was adapted to these determinants. Furthermore, the determinants were associated with the degree of implementation, and both users and non-users of the innovation were asked about possible determinants. In the Delphi study, consensus was defined as agreement among 75% of the experts on both the influence of a determinant and the direction towards which that influence tended (i.e. facilitating, impeding, or neutral). Results. From the initial 2239 abstracts, 57 studies were retrieved and 49 determinants were identified that affected (impeded or facilitated) the innovation process. The experts identified one other determinant. Seventeen studies had a more-or-less systematic design; the others did not. After three rounds, consensus was reached on the influence of 49 out of 50 determinants. Conclusion. The results of the literature review matched those found in the Delphi study, and 50 potentially relevant determinants of innovation processes were identified. Many of the innovation studies had several methodological flaws, such as not adjusting innovation strategies to relevant determinants of the innovation process, or that data on determinants were gathered only from non-users. Furthermore, the degree of implementation was evaluated in several ways, which made comparison difficult. © International Society for Quality in Health Care and Oxford University Press 2004; all rights reserved.