Disability insurance protects workers' income when they can't work due to illness, injury, or medical condition. A worker earning $100k/year goes on leave due to a serious illness. Their disability insurance replaces 50-70% of salary during recovery, typically for weeks to years. Disability insurance is offered as a group benefit (employer-provided) or purchased individually. Providers include UNUM, MetLife, Prudential, and state government (Social Security Disability). Managing DI involves underwriting (assessing risk), claims processing (evaluating applicants), and reserving (setting aside money for future claims).