We had a clean domain. Orders, customers, payments — all modelled carefully, all speaking the same language. Then we integrated with a payment provider. Six months later, the PaymentStatus enum had values like PSPCONFIRMED , PSPREJECTED_RETRY , and AUTHORISED_3DS . Our Order entity had a StripeChargeId field. Our service layer was calling MapFromStripeWebhookPayload() . And every developer who touched payments had to understand Stripe's object model before they could understand ours. The domain hadn't changed. But it had been contaminated. The Anti-Corruption Layer is the pattern that prevents this. Here's how it works and how to implement it in .NET. What Is the Anti-Corruption Layer? The term comes from Eric Evans' Domain-Driven Design . When two systems need to communicate, the boundary between them is dangerous.…