Definition · Plain-language
Standard operating procedure (SOP)
A standard operating procedure (SOP) is a controlled, documented set of step-by-step instructions that defines how a routine task is to be performed consistently and compliantly.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
Why SOPs exist
SOPs exist to remove ambiguity and variability from how tasks are performed. When a procedure is written down and agreed, the outcome no longer depends on an individual’s memory or interpretation; anyone trained on the SOP can perform the task the same way. This consistency is the foundation of both quality and compliance, because regulators expect that critical activities are governed by approved instructions. SOPs also preserve organisational knowledge, so a process survives staff turnover rather than living only in people’s heads.
SOPs as controlled documents
In a GxP setting an SOP is not just a helpful guide — it is a controlled document. That means it carries a unique identifier and version number, is formally reviewed and authorised before use, is distributed so that only the current version is in circulation, and is changed only through change control. Staff must be trained on it and the training recorded. Obsolete versions are withdrawn to prevent anyone working to outdated instructions. These controls are what give an SOP regulatory weight.
Writing effective SOPs
A good SOP is clear, unambiguous and written for the people who will actually use it. It states its purpose and scope, defines responsibilities, and lays out the steps in the order they are performed, including acceptance criteria and what to do when something goes wrong. Overly long or vague SOPs invite deviation because staff cannot follow them in practice. The aim is an instruction that a competent, trained operator can execute correctly every time, producing the same reliable result.
Key facts
At a glance
- Definition: documented step-by-step instruction for consistent, compliant task execution
- Primary benefit: reduces variability and error regardless of who performs the task
- Status in GxP: a controlled document, not an informal guide
- Controls: unique ID, version control, authorisation, training records, periodic review
- Changed via: formal change control
- Common inspection focus: evidence that staff are trained and follow current SOPs
Common misconceptions
What people often get wrong
Often heard: An SOP is just a helpful internal guide staff can update informally.
Actually: In GxP an SOP is a controlled document. It has a version number, is formally authorised, can only be changed through change control, and staff must be trained on the current version. Informal edits would breach document control.
Often heard: The most detailed, longest SOP is the best one.
Actually: Excessively long or vague SOPs are often unworkable and invite deviation. The best SOP is clear and unambiguous enough that a trained operator can follow it correctly every time, not merely the most exhaustive.
Often heard: Once written, an SOP never needs changing.
Actually: SOPs are periodically reviewed and updated as processes, equipment or regulations change. Working to an obsolete SOP is a common compliance failure, which is why old versions are formally withdrawn from use.
Going deeper
