This study consists of five international articles and an introductory background review. Its focus is on the nature and structure of teachers' pedagogical knowing. This study treats teachers' pedagogical knowing as a broad theoretical concept and as an extended practice. Based on a broad concept of teachers' pedagogical knowing, analyses of qualitative data are presented. The results show that the concept and practice of teachers' pedagogical knowing contains certain fundamental tensions inherent in teaching. Five stand out: care and respect for students, the compelling power of teachers' personal justifications, the absence of a shared code of practice, the struggles to balance teachers' public and private roles, and the basic uncertainty within the teaching profession.