There are numerous ways to setup multiple Magento stores that all share the same codebase and backend, but what method you use depends on your needs.

This article is written with cPanel in mind, though the methodologies listed below apply no matter what control panel you're using. You will need Magento 1.4.x or greater installed too.

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1. URL Structure
2. Shared Hosting Caveat
3. Adding Another Store In Magento
4. Parked Domain Method
5. Addon Domain Method
6. Sub Domain Method
7. Subdirectory Method
8. Managing Multiple Stores
9. Secure Checkout For Each Domain

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