A wildfire is any uncontrolled, non-structure fire that occurs in the wilderness, wildland, or bush.

Wildfires are common in various parts of the world, occurring in cycles. They are often considered beneficial to the wilderness, as many plant species are dependent on the effects of fire for growth and reproduction. However, large wildfires often have detrimental atmospheric consequences. Nine out of ten wildfires are reportedly caused by some human interaction; others are caused by natural events such as lightning strikes, volcanic discharges, etc.

Wildfires differ from other fires only by their extensive size; the speed at which it spreads out from its original source; its ability to change direction unexpectedly; and to jump gaps, such as roads, rivers and fire breaks. Wildfires generally do not involve properties; however, with extensive urbanization of wilderness, they can cause extensive destruction of homes and other property located in the wildland-urban interface, a zone of transition between developed areas and undeveloped wilderness.

The strategies of prevention, detection, and suppression strategies have varied over the years, but now incorporate techniques that permit and even encourage fires in some regions as a means of minimising or removing sources of 'fuel' from any wildfire that might develop.

Distinction from other fires

Fires start when an ignition source is brought into contact with a combustible material (e.g. peat, shrub, trees) that is subjected to sufficient heat and has an adequate supply of oxygen from the ambient air (see Fire triangle). The event that triggers ignition may be natural, such as a lightening strike, or an action of man.

File:2002 african fires nasa.png|thumb|right|250px|Satellite image of wildfires on the African continent in 2002, part of a presentation on NASA's World Wind program

Wildfires differ from other fires in that they take place outdoors in areas of grassland, woodlands, bush, scrubland, peat, and other woody materials that act as a source of fuel (or combustible material). Buildings are not usually involved, unless the fire spreads to adjacent communities and threatens these structures. Some of the defining characteristics of wildfires are the large area of burned land, upwards of to , and higher; the velocity of the burning front, which can as fast as in forests and in grasslands; and the ability of the burning front to unexpectedly change direction and to jump across fire breaks. The intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire. These factors make fires particularly dangerous: for example, in 1959 the Mann Gulch fire thirteen Smokejumpers died when they lost their communication links and became disorientated; the fire consumed 18 km² (4500 acres). In the Australian February 2009 Victorian bushfires, at least 173 people died and over 2,029 homes and 3,500 structures were lost when they became engulfed by wildfire.