Social Security defines disability as the “inability to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or has lasted or can be expected to last for a continuous period of not less than 12 months”. This means that you must be unable to perform certain types of work because of a medical impairment that has lasted or is expected to last for one year. In determining whether you can work, Social Security also considers your age, education and work experience.