Magento Multi-Source Inventory (MSI) is the inventory system built into Magento Open Source and Adobe Commerce. It tracks stock separately for each physical location, called a source, groups sources into stocks that websites sell from, reserves units at checkout, and suggests which location should ship every order.

Why MSI confuses so many store owners

Most people meet Magento Multi-Source Inventory by accident. They upgrade, open a product, and find "Quantity per Source" and "Salable Quantity" where a single stock number used to be. Then a customer says the website shows 8 units while the warehouse report says 11, and the questions start.

I have explained MSI to a lot of store owners and finance teams, and the confusion always comes from the same few ideas: sources, stocks, salable quantity and reservations. Once those click, Magento Multi-Source Inventory is logical and quite elegant.

This post explains each idea in plain language, with small worked examples.…