Book excerpt: Most of the Earth's surface is covered by water. Many aspects of our everyday lives and activities may be affected by water waves in some way. Sometimes, the waves can cause disaster. One of the examples was the tsunami that occurred in the Indian Ocean on 26 December 2004. This indicates how important it is for us to fully understand water waves, in particular the very large ones. One way to do so is to perform numerical simulation based on the nonlinear theory. Considerable research advances have been made in this area over the past decade by developing various numerical methods and applying them to emerging problems: however, until now there has been no comprehensive book to reflect these advances. This unique volume aims to bridge this gap.