If you have heard of ISO 9000, then it is most probably through ISO 9001, ISO 9002 or ISO 9003, the three quality assurance models from the ISO9000:1994 standard against which organizations can be certified. At some stage, you have probably wondered what the difference between them is. The answer is that the difference is simply one of scope.
ISO 9001 sets out the requirements for an organization whose business processes range all the way from design and development, to production, installation and servicing;
for an organization which does not carry out design and development, ISO 9002 is the appropriate standard, since it does not include the design control requirements of ISO 9001 - otherwise, its requirements are identical;
ISO 9003 is the appropriate standard for an organization whose business processes do not include design control, process control, purchasing or servicing, and which basically uses inspection and testing to ensure that final products and services meet specified requirements.
So, an organization chooses that its quality system be certified against ISO 9001, ISO 9002 or ISO 9003 according to the business processes covered by the quality system. There is no difference of quality ranking between the three standards