Solar activity is all forms of phenomena associated with the “active regions” on the Sun, which are associated with sunspots. Examples of solar activity are coronal mass ejections, flares, the 11-year-period solar cycle, energetic particles, and geomagnetic storms. Solar activity, although virtually impossible to forecast a month in advance, has succumbed to scientific methods on long time scales, much as seasonal climate forecasts are possible but weather forecasts beyond about 14 days are not. Moderately accurate solar activity forecasts on decadal time scales now seem possible. The workable methods fall into a class of prediction techniques called precursor methods, which have proved successful for two solar cycles.