Quest Diagnostics is a provider of diagnostic information services to patients and physicians through a network of laboratories and company-owned patient service centers.

It offers a range of services including clinical testing with gene-based and other esoteric tests, anatomic pathology services, life insurer services, clinical trial testing, and various healthcare information technology and diagnostic products. Quest Diagnostics provides its services to managed care organizations and other health insurance providers, clinicians, hospitals, retail healthcare providers, laboratories and governmental agencies, among others.

The company, along with its subsidiaries and branches, operates in North America, Asia Pacific, South America, and Europe. Quest Diagnostics is headquartered in Madison, New Jersey, the US.