The International Organization for Standardization develops and publishes International Standards.

Certification can be a useful tool to add credibility, by demonstrating that your product or service meets the expectations of your customers. For some industries, certification is a legal or contractual requirement.

ISO does not perform certification. ISO develops International Standards, such as ISO 9001 and ISO 1400, but is not involved in certification, and does not issue certificates. This is performed by external certification bodies.

Certification is the provision by an independent body of a written assurance (a certificate) that the product, service or system in question meets specific requirements.
Accreditation is the formal recognition by an independent body, generally known as an accreditation body, that a certification body operates according to international standards.