diff --git a/docs/dev/design/mc-base-currency-implementation.md b/docs/dev/design/mc-base-currency-implementation.md
new file mode 100644
index 0000000..a49f81b
--- /dev/null
+++ b/docs/dev/design/mc-base-currency-implementation.md
@@ -0,0 +1,110 @@
+# MC Base Currency Implementation Plan
+
+## Overview
+Switch the Mycelium marketplace from USD to MC (Mycelium Credit) as the base currency while preserving identical UX for USD users through 1:1 exchange rate.
+
+## Critical Requirements
+- **MC as Base**: All internal calculations use MC as reference currency
+- **USD UX Preservation**: Users selecting USD get identical experience to current system
+- **1:1 Exchange Rate**: 1 MC = 1 USD to maintain UX equivalence
+- **Backward Compatibility**: No breaking changes for existing functionality
+
+## Implementation Phases
+
+### Phase 1: Core Currency Service Overhaul
+- [ ] Update `CurrencyService::get_supported_currencies()` to make MC base currency
+- [ ] Change MC `is_base_currency: true` and `exchange_rate_to_base: dec!(1.0)`
+- [ ] Update USD `is_base_currency: false` and `exchange_rate_to_base: dec!(1.0)`
+- [ ] Recalculate all other currency rates relative to MC (not USD)
+- [ ] Update `CurrencyService::get_base_currency()` to return MC
+- [ ] Update `convert_amount()` method to use MC as base reference
+- [ ] Update `get_exchange_rate_to_base()` to use MC as base
+- [ ] Update `get_all_exchange_rates()` to use MC as base
+- [ ] Update `get_currency_stats()` base currency reporting
+
+### Phase 2: System-Wide Defaults Update
+- [ ] Change `CurrencyService` default_display_currency from "USD" to "MC"
+- [ ] Update user preference defaults in `UserPersistentData` from "USD" to "MC"
+- [ ] Update model builders default currency from "USD" to "MC"
+- [ ] Update controller response defaults from "USD" to "MC"
+- [ ] Update template fallback values from "USD" to "MC"
+- [ ] Update navbar service defaults from "USD" to "MC"
+
+### Phase 3: Service Layer Updates
+- [ ] Update `UserPersistence` default display_currency from "USD" to "MC"
+- [ ] Update `AutoTopUpService` USD references to use base currency
+- [ ] Update `InstantPurchaseService` USD references to use base currency
+- [ ] Update `OrderService` base currency references
+- [ ] Update `ProductService` base currency handling
+- [ ] Update `Wallet` service currency defaults
+- [ ] Update `PoolService` token references from "USD" to base currency
+- [ ] Update `ResourceProvider` base currency references
+
+### Phase 4: Controller Updates
+- [ ] Update `CurrencyController` base currency responses
+- [ ] Update `DashboardController` currency defaults and responses
+- [ ] Update `WalletController` currency handling
+- [ ] Update `OrderController` currency processing
+- [ ] Update `MarketplaceController` currency defaults
+- [ ] Update `PoolController` currency references
+- [ ] Update all hardcoded "USD" strings in controller responses
+
+### Phase 5: Model Updates
+- [ ] Update `MarketplaceCurrencyConfig` base_currency default
+- [ ] Update `Product` model base_currency defaults
+- [ ] Update `Order` model base currency references
+- [ ] Update `Transaction` model currency defaults
+- [ ] Update builder patterns to use MC as default
+- [ ] Update all model default values from "USD" to "MC"
+
+### Phase 6: Template Updates
+- [ ] Update hardcoded currency defaults in HTML templates
+- [ ] Update JavaScript currency handling
+- [ ] Update template variables and fallbacks
+- [ ] Ensure dynamic currency selectors work with MC base
+
+### Phase 7: Testing & Validation
+- [ ] Update unit tests to expect MC as base currency
+- [ ] Update integration tests for currency conversions
+- [ ] Test USD user experience preservation
+- [ ] Validate all currency conversion accuracy
+- [ ] Test edge cases and error handling
+- [ ] Performance test currency operations
+
+### Phase 8: Documentation & Migration
+- [ ] Update code comments referencing USD as base
+- [ ] Update API documentation
+- [ ] Create migration guide for existing data
+- [ ] Update configuration examples
+- [ ] Document exchange rate change process
+
+## UX Preservation Validation Checklist
+- [ ] USD users see identical prices to current system
+- [ ] Currency conversion works bidirectionally
+- [ ] All formatting remains consistent
+- [ ] User preferences persist correctly
+- [ ] Wallet balances display correctly
+- [ ] Transaction history shows correct values
+- [ ] Checkout process works identically
+
+## Risk Mitigation
+- **Data Migration**: Ensure existing user data migrates correctly
+- **API Compatibility**: Maintain backward compatibility
+- **Performance**: Monitor currency conversion performance
+- **Error Handling**: Comprehensive error handling for edge cases
+- **Rollback Plan**: Ability to rollback if issues arise
+
+## Success Criteria
+- [ ] MC is the internal base currency for all calculations
+- [ ] USD users experience no functional differences
+- [ ] All currency conversions work accurately
+- [ ] System performance remains acceptable
+- [ ] All tests pass
+- [ ] Documentation is updated
+- [ ] No breaking changes for existing integrations
+
+## Future Considerations
+- Exchange rate flexibility for future changes (1 MC = 10 USD, etc.)
+- Additional currency support
+- Multi-currency wallet support
+- Advanced currency conversion features
\ No newline at end of file