The emerging theory of negative imaginary systems is attracting increasing interest amongst control systems researchers because it captures a wide range of practical problems. Negative imaginary dynamics often arise as a simple fundamental consequence of Newton's second law of motion. Often control systems performance can be significantly improved, despite demanding robustness requirements and difficult dynamics, by directly exploiting system properties. The study of negative imaginary systems can lead to potential improvements in several engineering fields including areas of advanced technology such as nano-positioning systems, control of multi-agent dynamical systems, distributed network control, mechatronics and robotics among others. This work will develop new results in the theory of negative imaginary systems. These results will underpin controller design methods and controller tuning guidelines for this class of systems. The developed methodologies will be applied to several specific benchmark applications and case studies. Wide dissemination of the advantages of the negative imaginary concepts will be a key aspect of this work.