The implementation of CLIL as an educational innovation has not yet been intensively investigated. This study aims at identifying factors which are potentially influential for the implementation in four heterogeneous primary CLIL programs. Using participant observation and Grounded Theory Methodology, the results yield a hierarchical category system comprising properties of CLIL teachers, other stakeholders, and the CLIL program. The analysis suggests that initiations by single teachers are less likely to succeed in the long run than programs carried out over a longer period involving the school as a whole. Phase-specific characteristics suggests that the commitment of the leadership, sufficient resources and their exchange, as well as CLIL-related experience are pervasive overarching aspects. For new small-scale programs, an autonomous scope of action, the commitment of other stakeholders, the general workload and additional time are crucial, as is an official status of the innovation, while in established programs, evaluation, improvement and extension become increasingly relevant. Future research needs to test these hypotheses regarding their actual predictive power for a successful innovation. (submitted)