This book presents updated scientific issues, and future plans related to energy production technologies, and energy systems. The book focuses on the electrical energy. It includes selected topics that cover the following themes: 1. Energy technologies and production studies, 2. Energy security and optimization, 3. Stability of energy systems, 4. Technological reliability studies, 5. Bio-fuels and bio-economy, and 6. Miscellaneous topics. The book is therefore divided into six sections, each of which contains one of these themes. The secure and sustainable design and operation of energy systems is among the main targets of the book. Due to the multidisciplinary nature of the book, it is beneficial for educational and research purposes in interdisciplinary undergraduate and postgraduate curriculums. The book is also prepared for facilitating self-study of independent students. It is also valuable for engineers, economists, and decision makers for better understanding of the current and future of the considered theme.