The Social Security Administration uses a wide array of criteria and a multi-stage appeals process to determine if an individual qualifies for Social Security Disability Insurance (SSDI) or the Supplemental Security Income (SSI) programs. The basic definition of a qualifying disability is very simple: SSDI defines a qualifying disability as “the inability to engage in any substantial gainful activity (SGA) by reason of any medically determinable physical or mental impairment(s) which can be expected to result in death or which has lasted or can be expected to last for a continuous period of not less than 12 months.