Lock-ins of crop diversification can prevent cropping systems from becoming more diversified. Identification of success and failure factors, as well as enablers and drawbacks of crop diversification initiatives are thus important for upscaling crop diversification. A database was built from the 128 valid responses of the survey performed in 12 European countries. While the most important failure factors were economic (e.g., market conditions and amount of financial resources), the technological factors (e.g., availability of inputs, technical solutions) were also very important. The most important success factors were related to social factors (e.g., professional expertise and commitment of actors, general public interest). The three most frequently mentioned target outcomes of European crop diversification experiences were improved environmental sustainability, improved agricultural production stability and increased income.