With the emergence and general acceptance of online samples for market, opinion, and social research comes a responsibility to measure and ensure the quality of research results using such samples. A number of concerns about sample quality have been raised across the industry. They include concerns about: -Professional research participants who through various means try to maximize their survey opportunities -Inattentive if not deliberately untruthful research participants -The potential for duplicate research participants as online sample providers broaden their sources in search of more diverse samples and low incidence populations -Representativeness, that is, the degree to which research results accurately reflect the target population, however defined. This Guideline responds to those concerns by providing guidance on the operational requirements for the provision of online samples for market, opinion, and social research. It sets out methods to be used by online sample providers, buyers, and end clients to ensure that a sample meets widely accepted quality criteria. It is recommended reading for all stakeholders in the research process, from survey designers to data users.