We know the face of another person, and we can identify among thousands or even millions. Again, we are not able to speak and explain exactly how we recognize the person. We manage to bike, but it's hard to verbalize knowledge. Basic and often quoted idea is the concept of tacit knowledge ' we know more than we can say.' What, in fact, tacit knowledge? All we use it but we did not necessarily willing or able to easily articulate (Polanyi, 1967). In the organizational context, as human beings we use that knowledge does not necessarily have to be codified or articulated. This knowledge is known as tacit (silent, unspeakable, it is hard to verbalize but can be codified). The proportions of tacit knowledge is difficult to articulate practical because most of this knowledge is not possible to translate verbal or introspective (Sensiper & Leonard, 1998). Tacit knowledge has the following characteristics: A source of knowledge, as the basis for the collection, generation and dissemination; It is possible to codify (in practice, individuals and organizations), we learn from the successful application of tacit knowledge; It can be reduced to simple principles ; We tend to associate unidirectional tacit knowledge with intelligence that can be measured, but it is not so ; Tacit knowledge is, first, the general level of ability that makes the difference between more and less successful individuals (Wagner & Sternberg, 1985). People are not often aware of that tacit knowledge have the potential of which it has knowledge. Tacit knowledge often consists of habits and culture that we do not recognize ourselves. From the point of view of knowledge management problems, the concept of tacit knowledge refers to knowledge that is available only to the individual and that are difficult to transfer to others, in contrast to explicit that it is easier to transfer. The process of transferring tacit to explicit knowledge is called codification or articulation. Tacit aspects of knowledge are those aspects that can not be codified but can be transferred through training and exercise, or they can gain experience. Tacit knowledge can be described as know-how, as opposed to know- what (you know what) (facts), know-why (science) or know who (know who) (networking). This knowledge includes learning and skills, but not in the form in which they may write. Tacit knowledge is knowledge which involves understanding, intuition and hunches, it is the knowledge that in our 'heads', but not formalized, expressed in numbers or letters. It depends on the personality of its experience, emotion, intuition. Polanyi (1987) makes a distinction : explicit knowledge - objectified in a variety of technologies, documents, procedures, projects, drawings, databases, etc.. Explicit knowledge is objektizovano, rational and mostly technical ; implicit knowledge - (quietly, silently) are increased and accumulated in each individual as a means of his individual abilities, intellect, and culture. This knowledge is always more than we can formally express and measure. Tacit knowledge contributes to the ' intangible property ' (attitudes, imagination, intuition...). There are controversies in the relationship between theory and practice in the field of pedagogy, where there is no harmony or the final decision on how to model this relationship. From our perspective, the theory of science education become ' promising ' if they face and connect with diversified pedagogical and professional practices and the specific circumstances in which it takes place. The identity of teachers and tacit knowledge touching the concept of 'taking the role and adoption ' (roletaking, Mid 1934). The concept involves the use of ' self' in a reflexive dialogue with them until the fulfillment of the role. Different ' I' that is reflective inner self, and the 'self ' which is visible social self. Both of these processes and actions come together during the download and the role of exercise, so reflexive 'I' managed and run by active 'self ' through interaction. Self, ' self ' is a social structure (Mid 1934), and reflective thinking shapes of the ' self' by allowing the kreairaju and realize the role. 'Taking part ' - the self is able to respond and struktuiše own experience (self). This concept is the same as the concept of reflexivity - in - action Donald Shona, in the sense that it means 'to see ourselves as others see us maybe, and adjust behavior accordingly.' Sean's idea that 'our knowledge - in our actions,' affirms the importance of practical, tacit and implicit knowledge - that teachers rely in their daily work. Such an epistemology of practice has been established in order to demystify the professional knowledge and highlight the importance of direct teaching practices for the development of professional identity of teachers. .