Lightning ignition of wildland fuels plays a major role in the maintenance and evolution of ecosystems. Lightning not only ignites fire but also weakens trees, facilitating insect and disease attack, causes physical damage, and kills trees and groups of trees (Taylor, 1973). Lightning ignition may also play a large part in forest response to global climate change. Fire can also alter lightning. Cumulus clouds, called pyrocumulus, can be formed under the proper conditions by large fires. Pyrocumulus clouds have a high proportion of positive cloud-to-ground lightning, the opposite of lightning from a 'normal' cumulus (Latham, 1991). One hypothesis for the cause is an interaction between the earth's electric field and the fire (Vonnegut et al., 1995). Smoke from fires can apparently cause inverted storms over a large area (Lyons et al., 1998a). In this chapter, we will show how the predominant mechanism for lightning ignition works and how this knowledge can be used for forest health and fire management. We will discuss worldwide lightning and fire patterns. Before discussing ignition and other consequences, a brief introduction to lightning is supplied; it is a subject not usually discussed in a forestry curriculum.