This guide is a complete working treatment of the Social Security disability system for claimants, their families, and the representatives and lawyers who handle these cases. Part I separates the two programs and explains the insured-status and resource rules that determine which one applies and what it pays. Parts II and III work the statutory definition and the five-step sequential evaluation in detail, including the substantial-gainful-activity thresholds, the severity screen, the listings, and residual functional capacity. Part IV covers the medical-vocational grid, the age categories that quietly decide a large share of cases, and skill transferability. Part V is evidence: what the 2017 rule change did to treating-source opinions, what persuades adjudicators now, and how symptoms and daily activities are evaluated. Parts VI through VIII cover the four levels of appeal, the hearing and vocational-expert examination where most cases turn, and substantial-evidence review in federal court. Parts IX through XII cover money, work incentives, continuing reviews and overpayments, and children's claims, closing with a stage-by-stage verification list and an authorities table.