How do method validation, verification and transfer differ?

Why

The three answer different questions about the same procedure. Validation, described in ICH Q2(R2), asks whether the procedure measures what it should with enough specificity, accuracy and precision across its range. It is done when a procedure is developed or significantly changed.

Verification applies when someone else already validated it. US regulation says that if a method is in the USP or another recognized reference, citing it is enough, but its suitability must still be verified under actual conditions of use. A pharmacopoeial impurity method might not separate an impurity unique to your synthetic route, so verification checks the parts most likely to differ.

Transfer moves a validated procedure between laboratories. Q2(R2) says transfer can involve partial or full revalidation or comparative analysis of representative samples, and co-validation across sites can satisfy transfer too. WHO's 2022 technology transfer guideline lists approaches such as comparative testing, co-validation and paper-based knowledge transfer, chosen on risk, with a protocol that defines design and acceptance criteria agreed before execution.

The terms blur in practice. A transfer that fails may reveal that the original validation never covered a factor that differs between sites, which sends you back to robustness and validation rather than retesting the transfer.