We've known since the game was announced that players would eventually be able to transfer Pokémon from older titles to the upcoming Sun and Moon, which will be released on November 18th. The only way to do so is through the cloud-based Pokémon Bank 3DS app, which will get an update in January 2017 allowing you to port your old monsters into the new game. To sweeten the deal and better connect the franchise, they're including something else when you connect to the app: A Pokédex that tracks all the Pokémon you've caught across every 3DS game in the series.
Sadly, that means the other games, even the Virtual Console re-releases of the classic trio on the handheld system, will be left out of the Pokédex. There's plenty of time between Sun and Moon's launch in two months and the update in January, so get catching. Come the beginning of 2017, challenging players to fill the Pokédex's comprehensive list may breathe new life into the old games.
If you're not savvy on the bank's transfer rules, here's a graphic rundown. Note that the black-and-white "Poké Transporter" option is a one-way ticket, so think carefully before you send your old friends to Sun and Moon: