How do you create a test strategy for a product or organisation?

A test strategy describes how we achieve quality across the organisation, not for one release. I start with business goals, risk appetite and compliance needs, then map the product architecture and delivery model. I define quality objectives and measurable targets, such as escaped defect rate, lead time and reliability. I set the testing approach per level: ownership of unit, component, contract, API, UI, performance, security, accessibility and production monitoring; the tooling and environments; data and privacy rules; quality gates in the pipeline; metrics and reporting; and roles and skills. Then I make it a living document reviewed quarterly with results.