This study was aimed to explore the interaction between effective physics teacher characteristics, from teachers&rsquo / and students&rsquo / shared perceptions and students&rsquo / motivation. The thesis included two main parts. The first part was quantitative and the characteristics were identified. The second part was qualitative and the characteristics were used as criteria to select two case teachers and the interaction between their characteristics and students&rsquo / motivation was investigated. The questionnaire, in the quantitative part, was administered in 3 regions of Turkey and 3 cities for each region including 214 high school physics teachers. There were two different questionnaires, derived from the quantitative part, to select the two case teachers for the qualitative part. The qualitative data included interviews with the two case teachers and their students, field notes, and videos. The data in the quantitative part was analyzed by descriptive statistics. Findings revealed that there were 38 effective physics teacher characteristics affecting students&rsquo / motivation in physics within 8 categories as perceived by teachers and students. The characteristics were important in terms of students&rsquo / motivation as perceived by teachers more than as perceived by students. The teachers&rsquo / subject matter knowledge and their personal characteristics were the two categories that mostly affected the students&rsquo / motivation. The data in the qualitative part was analyzed by cross case analysis. The findings revealed that the positive characteristics increased students&rsquo / motivation, when the teachers exhibited them. When the teachers did not display the positive characteristics, the students&rsquo / motivation decreased. If teachers exhibited the negative characteristics in a positive way it was likely to increase students&rsquo / motivation. The qualitative part enhanced results of the quantitative part in that it enlightened the way that those characteristics affected students&rsquo / motivation and what would cause if those characteristics were not exhibited or were exhibited negatively.