Recently, high-power driver linacs have been widely proposed in Asia, Europe and North America to generate various useful secondary particles by bombarding a certain target with energetic light ions. For such a large-scale linac, the beam dynamics is most complicated in the low- and medium-energy part due to the space-charge effects. This book focuses on the conceptual studies performed with respect to the front-ends of the three accelerator-based facilities planned by Germany, the European Union, and a worldwide cooperation, respectively. To fulfill the different project goals, e.g. hands-on maintenance, high reliability, easy upgradeability, and minimum costs, new strategies and approaches, e.g. the so-called "BABBLE" procedure, the special transverse and longitudinal matching techniques, and the application of adjustable rebunching cavities, have been developed and proposed for leading to efficient designs of the adopted radio-frequency quadrupole accelerators and H-type drift-tube linacs. This work can be of value to the linac colleagues as well as other scientists who are interested in using an accelerator as a driver for their research and applications.