A resource allocation scheme (usually for memory). First Fit fits data into memory by scanning from the beginning of available memory to the end, until the first free space which is at least big enough to accept the data is found. This space is then allocated to the data. Any left over becomes a smaller, separate free space.

If the data to be allocated is bigger than the biggest free space, the request cannot be met, and an error is generated.

Compare Best Fit.