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What is this type of risk-free investment called?
This is what is called a Structured Product.  The linked page gives an overview of the relative pros and cons.  They tend to hold the bulk of funds in bonds and then used equity index futures and other derivatives to match returns on the S&P, or other indices tracked.  All combine to provide the downside protection. Note that your mother did not receive the dividends paid by the constituent companies.  She only received the capital return. Here is a link to Citigroup (Europe) current structured product offerings. Here is a link to Fidelity's current offerings of structured products. Here is Investopedia's article detailing the pitfalls. The popularity of these products appears to be on the wane, having been heavily promoted and sold by the providers at the time your mother invested.  Most of these products only provide 100% protection of capital if the market does not fall by a specified amount, either in successive reporting periods or over the life of the product.  There are almost as many terms and conditions imposed on the protection as there are structured products available.  I have no personal experience buying this type of product, preferring to have the option to trade and receive dividend income.