Disability Insurance, often called DI or disability income insurance, or income protection, is a form of insurance that insures the beneficiary's earned income against the risk that a disability creates a barrier for completion of core work functions. For example, the worker may be unable to maintain composure in the case of psychological disorders or sustain an injury, illness or condition that causes physical impairment or incapacity to work. DI encompasses paid sick leave, short-term disability benefits (STD), and long-term disability benefits (LTD). The same concept is instantiated in some countries as income protection insurance.

In the late 19th century, modern disability insurance began to become available. It was originally known as "accident insurance". The first company to offer accident insurance was the Railway Passengers Assurance Company, formed in 1848 in England to insure against the rising number of fatalities on the nascent railway system. It was registered as the Universal Casualty Compensation Company to:

The company was able to reach an agreement with the railway companies, whereby basic accident insurance would be sold as a package deal along with travel tickets to customers. The company charged higher premiums for second and third class travel due to the higher risk of injury in the roofless carriages.

Those whose employers do not provide benefits, and self-employed individuals who desire disability coverage, may purchase policies themselves. Premiums and available benefits for individual coverage vary considerably between companies, occupations, states and countries. In general, premiums are higher for policies that provide more monthly benefits, offer benefits for longer periods of time, and start payments of benefits more quickly following a disability claim. Premiums also tend to be higher for policies that define disability in broader terms, meaning the policy would pay benefits in a wider variety of circumstances . Web-based disability insurance calculators assist in determining the disability insurance needed.

High-limit disability insurance is designed to keep individual disability benefits at 65% of income regardless of income level. Coverage is typically issued supplemental to standard coverage. With high-limit disability insurance, benefits can be anywhere from an additional $2,000 to $100,000 per month. Single policy issue and participation (individual or group long-term disability) coverage has gone up to $30,000 with some hospitals.

Business Overhead Expense (BOE) coverage reimburses a business for overhead expenses should the owner experience a disability. Eligible benefits include: rent or mortgage payments, utilities, leasing costs, laundry/maintenance, accounting/billing and collection service fees, business insurance premiums, employee salaries, employee benefits, property tax, and other regular monthly expenses.

In most developed countries, the single most important form of disability insurance is that provided by the national government for all citizens. For example, the United Kingdom's version is part of National Insurance; the United States' version is Social Security (SS): specifically, several parts of SS including Social Security Disability Insurance (SSDI) and Supplemental Security Income (SSI). These programs provide a floor beneath all other disability insurance. In other words, they are the safety net that catches everyone who was otherwise (a) uninsured or (b) underinsured. As such, they are large programs with many beneficiaries. The general theory of the benefit formula is that the benefit is enough to prevent abject poverty.

One of the most common reasons for disability is on-the-job injury, which explains why the second largest form of disability insurance is that provided by employers to cover their employees. There are several subtypes that may or may not be separate parts of the benefits package: workers' compensation and more general disability insurance policies.