Teachers are playing a central role in our education system. They are the link between theory and practice and act both as mentors and mediators. As the world is developing rapidly, for students it is important to have a mentor, who provides education that brings knowledge and everyday life together.4 Therefore professional development after preservice teacher education at university becomes extremely important to meet today’s requirements of the European education system. It is further crucial to consistently renew the initial teacher education through in-service training to conform teacher education to the latest educational standards of a rapidly changing world. As stated by Jarvis and Pell5 the cognitive level achieved by students is related to the competence of their teachers. Present professional development programs provide an opportunity for teachers to pay more attention on the development of students’ high level skills. Many of these educational activities are based on inquiry based approaches and help teachers to get involved in inquiry based science. In effective professional developments teachers are treated as adult learners. Most of the teachers expect to learn about new theories of learning or new instructional strategies. However, they do not expect their previous practices to be questioned or to be lectured about their status of knowledge.6 Applying the “teacher as adult learner” paradigm, activities like case studies, role playing, simulations, and selfevaluations are more helpful than giving lectures to teachers. In this manner the teachers have the chance to get familiarised with the new inquiry ideas and can construct their own understandings. A further main element addressed in professional developments is the “Socio-cultural” paradigm. The majority of teachers remain relatively autonomous in their classrooms and collaboration with peers of a certain subject is very rare.7 Consequently, the PDs reveal the advantages, the challenges, and the knowhow of collaborative learning, which is an essential component of any learning. Equally important for teachers is the ability to resolve cognitive dissonance they experienced occasionally. With help of the Pathway training activities, teachers have the opportunity to practice occurring situations in the classroom, and are given the time, structure, and support to think about the dissonance experienced. Through this they get the opportunity to experience the same skills, knowledge, and thinking habits as their students. If teachers decide to change their way of education and to introduce the inquiry approach, they have to perform a change in their behaviour and to adapt a new culture and philosophy. Certainly, for science teaching that motivates and engages every type of student, the process starts with the teachers’ decision to use inquiry based teaching. The essential part of the teacher is to develop an understanding of scientific inquiry and to learn how to accomplish it. Professional developments implement this part of the changing process and apply the main characters important for being a successful teacher in IBSE. The desired effective science teacher competencies consist of the Subject Matter Knowledge (SMK), the Pedagogical Knowledge (PK) and the Pedagogical Content Knowledge (PCK). The SMK aims to link the knowledge of subject specific inquiry approach possibilities, the competencies related to the nature of science including inquiry knowledge and skills, the interconnection of different subjects and the competence to motivate the students with general background knowledge. Competencies teachers should be able to access are described by the Pedagogical Knowledge. It is a must for a successful IBSE teacher to have various teaching strategies available, to improve every teaching aspect with advanced in-service education and to be able to reflect their own teaching methods. To use IBSE, teachers should have a distinct Pedagogical Content Knowledge in a wider sense. Therefore they have to have the competencies to match the inquiry focused lesson with the existing topics, methods and materials, to use additional hands-on materials within collaborative laboratories, science centres and museums and to address the students’ common sense knowledge and learning difficulties. Further, they should have sound competencies in the use of ICTs (Information and Communication Technologies) and ETs (Educational Technologies), in which situations these can be used and be able to connect IBSE with the curricular materials. Holding these competencies teachers can use authentic learning experiences (best practices), which are interesting, engaging and are relevant to their successful classroom practice. These principles (underpinning essential education in science) will help students to understand the scientific aspects of the world around them, and let them make information based logic decisions about the applications of science as well. Teachers who were involved in an inquiry based training program should be able to encourage students to do science and to interact professionally with peers and experts. Furthermore they should be able to help students to solve problems on their own, to assess their students continuously using a variety of alternative assessment methods, to customize the new activities according to their teaching needs, and to align the inquiry with the concepts taught or discussed in the classroom.