This book reports the findings from the tri-national video study Quality of Instruction in Physics (QuIP). Within the scope of the QuIP study, physics instruction was investigated in a total of 103 classes from-Finland, North Rhine-Westphalia (Germany) and German-speaking Switzerland. The main aim was to identify typical patterns of physics instruction of the three samples and to investigate conditions under which these patterns are successful with respect to students' learning, interest and motivation. Among others instructional characteristics, the quality of students' practical work, successful patterns of sequencing, the subject matter structure and teaching strategies were investigated by means of analyses of video-recorded lessons. Variables external to instruction that were investigated included teachers' professional knowledge and students' cognitive abilities. The study followed a pre-post-design with data collection prior to and after an instructional unit on electrical energy and power. The results are well in line with the findings from large-scale international studies indicating a particularly successful instructional pattern in Finland. A comparison of characterisation of instruction in comparison between the three countries reveals important findings for the improvement of the teaching and learning of physics in secondary school education.