The concept of open innovation is currently one of the key issues regarding the innovative development of micro, small, and medium enterprises (SMEs). It has been the subject of research both in the theoretical and empirical context. At present, there is no unambiguous definition conceptualizing the conceptual scope of open innovation (OI). However, enterprises do not always decide by themselves to be open to the environment. Therefore, determinants are important, as they encourage enterprises to greater openness, which can be treated as a key element of a value chain for SMEs, contributing to their innovative development. Classification of these determinants (also named as factors) is very poor in the literature. Generally, internal and external determinants are identified. Authors decide on the selection of these factors and their division by themselves. The research presented in this article has indicated the existence of several significant regularities. Firstly, larger entities are more likely to use the OI concept. Secondly, market determinants are the most important for the use of OI among SMEs. Thirdly, both internal and external determinants have a huge impact on the application of the OI concept, with external determinants being more significant for smaller rather than larger entities. The conclusions drawn were a consequence of the assumed aim of the article: The assessment of the influence of determinants that affect the use of the OI concept among SMEs in Poland.