The ADA attempts to provide a comprehensive solution to discrimination against the disabled, including employment, access to governmental services, and access to private services and premises. Many core provisions of the ADA are derived from section 504 of the Rehabilitation Act of 1973. The ADA covers more employers, however, because section 504 was limited to employers who did business with the government. The ADA covers all workplaces with 15 or more employees. Unlike OSHA, which excludes governmental entities, the ADA covers both government and private businesses. Although these included most large employers - universities, medical institutions, and governmental entities themselves - many small businesses were exempt. Section 504 of the Rehabilitation Act remains good law and plaintiffs often plead the Rehabilitation Act along with an ADA claim when the defendant is covered by both.

The most profound shift in moving from Section 504 to the ADA is the change in the underlying statutory presumptions. Section 504 is a remedial statute that provided standards to judge whether a given individual was the victim of discrimination. It allows employers to use medical examinations and inquiries to determine the status of a potential or current employee's medical condition, including disabilities, and provides sanctions if this information is used improperly. The ADA presumes that employers will discriminate against disabled individuals if they have information about the employee's disability. It seeks to prevent discrimination by limiting the employer's access to information, as well as providing legal remedies for victims of discrimination. It is this shift from nondiscrimination to non-inquiry into disability that changes traditional occupational medicine practice.

The best statement of the broad reach of the ADA is from the congressional findings in the statute itself.