The ADA applies to individuals with disabilities that substantially limit one or more major life activity. The ADA covers people who—

• Are deaf, blind or use a wheelchair,
• Have physical conditions such as epilepsy, diabetes, HIV infection, or severe forms of arthritis, hypertension, or carpal tunnel syndrome, and
• Have mental impairments such as depression, bipolar disorder, and mental retardation.

The following conditions are NOT covered under the ADA:

• Environmental, cultural, and economic disadvantages
• Homosexuality and bisexuality
• Pregnancy
• Physical characteristics
• Common personality traits
• Normal deviations in height, weight or strength

The purpose of Title I of the Americans with Disabilities Act is to ensure that employers provide reasonable accommodations to individuals with disabilties thereby protecting their employment rights. Rights are protected during the application process, hiring, firing, wages, training, promotions and all other aspects of employment. Employers covered by the ADA must ensure that people with disabilities—

• Have an equal opportunity to apply for and work in jobs for which they are qualified.
• Have an equal opportunity for promotions.
• Have equal access to benefits.
• Are not harassed because of their disability.

Title I of the ADA applies to private employers with 15 or more employees, State and local governments, employment agencies and labor unions. When the ADA went into effect, the Equal Employment Opportunity Commission (EEOC) was tasked with issuing regulations and enforcing Title I of the ADA. The EEOC advised employers that when determining an employee's impairment, the decision should be made without considering steps taken to mitigate the disability.

However, in 1999 The Supreme Court ruled in three cases, known as The Sutton Trilogy, that individuals should be evaluated in their mitigated state. Essentially the Supreme Court ruled that if a person is taking measures to correct or mitgate the physical or mental impairment, the effects of those measures must be taken into account when judging whether the person is disabled. Because of the Supreme Court rulings, the EEOC rescinded the parts of its Title I regulations dealing with mitigating measures and revised its Technical Assistance Manual on Title I.

As a result of the Supreme Court rulings, some individuals were punished for taking steps to mitgate their disabilities or impairments. The Amendments Act of 2008 overturns the Sutton cases and all lower court opinions based on the Sutton precedent. Under the Amendments Act, the original definition of disability in the ADA remains the same, but the definition is to be interpreted broadly and not consider mitigating measures when making the disability determination.

The Rehabilitation Act of 1973 prohibits discrimination of individuals with disabilities by recipients of federal funding. Part of the Americans with Disabilities Act is based on Section 504 of the Rehabilitation Act. In the Amendments Act, Congress included an amendment to the Rehabilitation Act whereby the term "disability" in the Rehabilitation Act now has the same meaning as in the ADA act.