The purpose of this study was to determine perceptions of students, teachers and parents concerning English-medium instruction and their perceptions of English as a foreign language. The research design of the study comprised a nation-wide questionnaire survey and individual interviews. The sample for the survey consisted of 982 students, 383 teachers and 988 parents in 42 Anatolian high schools across 32 provinces in Turkey selected using statified and criterion sampling. The participants of the interviews were six students, four teachers and four parents. Two distinct instruments were used for data collection / a survey questionnaire containing five-point Likert scales and open-ended questions / and a semi-structured interview schedule. To analyze quantitative data, descriptive statistics, one-way ANOVA and bivariate correlations were conducted. The qualitative data of the interviews and open-ended questions were analyzed via content analysis. Results indicated that students, teachers and parents do not favor English-medium instruction at secondary education. Regardless of their position on English-medium instruction, participants underscored problems of implementation of English-medium instruction at Anatolian high schools. A positive correleation was found between perceptions of English and perceptions of English-medium instruction for each group. Results also showed that all groups perceive English positively as a foreign language, and support the teaching and learning of English. According to students&amp / #8217 / and teachers&amp / #8217 / perceptions, English-medium instruction influences the instructional process in math and science in Anatolian high schools, and poses problems particularly in the learning of the subject matter.