The fundamental pioneering ideas about student-centered, inquiry-based learning initiatives are differing in Europe and the US. The latter had initiated various top-down schemes that have led to well-defined standards, while in Europe, with its some 50 independent educational systems, a wide variety of approaches has been evolved. In this present paper, we portray a European bottom-up initiative, "PATHWAY to Inquiry Based Science Education," to define a basis for learning initiatives and to meet current challenges to access learning, to share knowledge and establish competences in learning communities. Our approach was designed to act as bottom-up catalyst by mobilizing teacher communities to (further) foster inquiry. Of a sample of 10.053 science teachers from 15 European countries (incl. Russia), about 5060 provided empirical support for our teachers' professional development initiative. The response pattern portrayed teachers' preferences and pointed to potential needs in professional development (PD) efforts. On average, our sample reported an altogether 11 years' period of teaching practice in general but just 2-3 years of experience in inquiry-teaching. In the view of that, consequences for professional development (PD) initiatives are discussed.