Purpose of the paper: This research has a twofold purpose. First, it aims to identify open innovation practices (OIP) used by empirical studies in the contextof the open innovation (OI) field. Second, it aims to test the inverted U-shaped relationship between the breadth of OIP and innovation performance.Methodology: We followed two steps, conducting: a) a bibliographic analysis to identify the OIP already used in empirical studies; b) an empirical analysis with a sample of 184 Italian firms to test the relationship between the breadth of OIP and innovation performance, and the moderating role of internal R&D over the mentioned relationship.Findings: The research identifies 16 OIP used by empirical studies and suggests that there is an inverted U-shaped relationship between the breadth of OIP and innovation performance. Furthermore, we did not find a moderating effect of the internal R&D on the above-mentioned relationship.Research limits: The empirical analysis does not consider the effect of the single OIP. Then, our sample is heterogeneous involving different sectors and firm sizes. We acknowledge that innovation management changes depending of the sector's features. Future studies could focus on specific sectors to further develop our understanding on this topic.Practical implications: The research helps to understand: a) what are the OIP that firms can exploit to innovate, b) how literature has used these OIP in empirical studies, and, c) if too much openness, in terms of practices, is beneficial for the firm's innovativeness or not.Originality of the paper: The study offers an original and comprehensive view of openness based on OIP given that most of the empirical studies on OI focused on external sources of knowledge, rather than on practices. As a consequence, the variable breadth of OIP, that is the number of practices established by firms to innovate, is proposed. So, we position our paper within the main inbound OI literature proposing an alternative and complementary view of openness with regard to knowledge acquisition.