Research has linked optimism to higher levels of subjective well-being, to positive mood and good morale, to perseverance and effective problem solving, to achievement and success in a variety of domains, to popularity, to good physical health, to reduced suicidal ideation, and even to long life and freedom from trauma. In this chapter, we review what is known about one cognate of optimism—“explanatory style,” how people habitually explain the causes of events that occur to them. We trace the history of explanatory style research, focusing on the neglected question of the origins of explanatory style. Finally, we conclude by addressing issues that need to be considered by positive psychologists doing research on explanatory style. Research still focuses too much on negative outcomes, ignoring the premise of positive psychology: What makes life most worth living needs to be examined in its own right.