In telecommunications and computing, a product or technology is backward compatible (BC) or downward compatible if it can function properly given input generated by, or meant for, an older product or technology, such as a legacy system. If products designed for the new standard can receive, read, view or play older standards or formats, then the product is said to be backward-compatible; examples of such a standard include data formats and communication protocols. Modifications to a system that do not allow backward compatibility are sometimes called "."

In telecommunications and computing, a product or technology is backward compatible (BC) or downward compatible if it can function properly given input generated by, or meant for, an older product or technology, such as a legacy system. If products designed for the new standard can receive, read, view or play older standards or formats, then the product is said to be backward-compatible; examples of such a standard include data formats and communication protocols. Modifications to a system that do not allow backward compatibility are sometimes called "."