This book provides principles on content analysis and its application into development of nursing theory. It offers clear guidance to students, lecturers and researchers to gain a deeper understanding of the method of content analysis, its implementation into their own research and criteria of trustworthiness evaluation. The book is written in user-friendly language with provided research examples and cases, and the content is illustrated by figures and tables. The authors offer their expertise in providing a well thought through explanation of content analysis in didactical style, which will enhance university education. The book includes highly experienced researchers who have published articles on content analysis and the trustworthiness of the method with more than 10 000 citations. Divided into two parts, this book explores the application of content analysis into nursing science. The first part presents the philosophical position of content analysis, inductive and deductive methods of using content analysis, trustworthiness of the method, and ethical consideration of using content analysis. The second part informs on the theory development based on content analysis, conceptualization of the concepts of content analysis into generation of items and instrument development, and statistical testing of a hypothetical model. The last chapter shows a new approach to using content analysis in systematic reviews and quality evaluation of methodology within systematic review process. The book is an essential tool for nursing science, providing instruction on key methodological elements in order to provide rigorously conducted empirical research for clinical practice and nursing education.