This book presents the proceedings of the 5th International Colloquium "Transformer Research and Asset Management," held in Opatija, Croatia, on October 9-12, 2019. The papers chiefly focus on three groups of topics: 1.  Numerical Modeling: Electromagnetic fields-Coupled fields-Transients-Numerical modeling in design 2. Materials, Components and New Technologies: Insulating materials-Magnetic materials and transformer noise-Transformer components-New transformer technologies 3. Transformer Lifecycle Management: Diagnostics and monitoring-Failure-Asset management-In-service experiences. The Colloquium was organized by the Croatian National Committee of CIGRE together with the Faculty of Electrical Engineering and Computing in Zagreb and the Centre of Excellence for Transformers