Pokémon Bank now supports Ultra Sun and Moon
Nintendo has recently released an update for the Pokémon Bank application, which allows support for Pokémon Ultra Sun and Moon, making the transfer of any Pokémon you have in storage easy for the new titles. Pokémon Bank is a subscription service which costs $4.99 per year, and supports titles from Pokémon X and Y, offering storage for 3000 Pokémon.
Poké Transporter now also supports the eShop versions of Pokémon Gold and Silver, where you can transfer Pokémon between these older titles to the newer ones like Sun and Moon. Carrying over Pokémon is strictly a one-way transfer, however (unlike Pokémon Bank), so they can't be transferred back to their original games.