Link is the rule that lets you plug a card sideways into one of your Digimon, paying its cost during your main phase, as long as the Digimon meets the link requirements. The linked card grants its bonuses without taking up a separate spot on the board, effectively upgrading a body you already have. Building around Link means matching requirements early so your midgame plugs are free choices, not dead cards.
10-1-1. A link is a rule where a card with [Link] can link by plugging it in sideways into one of your specified Digimon on the field according to the link requirements. A card from the hand or battle area can be linked to a Digimon in the battle area by paying the cost as part of the main phase actions. (For details, refer to 6-5 "Main Phase") 10-1-2. Link Rules 10-1-2-1. If a card already has stacked cards, the new card is plugged in at the bottom. 10-1-2-2. A card plugged in sideways for a link becomes a link card. (For details, refer to 4-7 "Link Cards") 10-1-2-3. If an immediate-type effect triggers when linking would occur, it will trigger immediately after the card is revealed and the Digimon to be linked is chosen during the link procedure. (For details, refer to 15-8-5 "Immediate-Type Effects")
Comprehensive Rules §10-1 — official rules page
From Bandai's card rulings. Each links to the card it was asked about.
Can I use this card's <On Play> <When Digivolving> effect to link a card that doesn't have <Link Keyword>?
No, you can't.
Ruled Apr 4, 2025 · asked about Globemon (BT21-023)
Can I use this card's <On Play> <When Digivolving> effect to link a card that doesn't have <Link Keyword>?
No, you can't.
Ruled Apr 4, 2025 · asked about Charismon (BT21-073)
If a Digimon's maximum links is increased using <Link+ 1> and has a total of 2 link cards including this card, then it would be removed from the battle area, can I choose from among those cards to trash for this card's <Link Keyword> effect?
Yes, you can choose 1 card from among that Digimon's link cards and trash it.
Ruled Apr 4, 2025 · asked about Charismon (BT21-073)
Can I use this card's <Delay> effect to link a card that doesn't have <Link Keyword>?
No, you can't.
Ruled Apr 4, 2025 · asked about App Link (BT21-097)
Can I use this card's <When Digivolving> <When Attacking> effect to link a card that doesn't have <Link Keyword>?
No, you can't.
Ruled Apr 4, 2025 · asked about Gaiamon (BT21-101)
10 cards carry this keyword:
Rule text © Bandai, quoted from the official Comprehensive Rules for reference. Combalo is not affiliated with Bandai.