Book excerpt: Since the publication of Robert Pianta's 2001 handbook on the quality of the teacher-student relationship, much has been accomplished and research contributions have multiplied from different authors and countries. This testifies to the richness and continuous evolution of this field of research. The quality of the teacher-student relationship has been recognized as an important factor in the psychological development of students and seems to increase their adjustment to the school context. A good quality of relationship, according to attachment theorists, is characterized by closeness, affection, and respect. In this direction, the teacher can offer a relational context that can support the child in their learning processes and psychological development, preventing negative outcomes. The research focused on defining the salient features of this educational relationship and refining tools that could collect the perceptions of students and teachers, trying to identify the possible outcomes associated and the mechanisms involved.