Prognosis has dominated recent low back pain (LBP) research because of the lack of disease pathological explanations of LBP that lead to safe and effective treatments in many patients; the hazards of overdiagnosis and overtreatment; and the potential for beneficial outcomes in patients if treatment approaches are carefully matched to the likelihood of recovery, recurrence, or persistence, or the likely effect of specific treatments. This chapter uses examples from each of the four types of prognosis research to illustrate how prognosis research has contributed to understanding LBP and provided evidence to inform classification and treatment of patients with LBP.