Illumination is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Counter target artifact or enchantment spell. Its controller gains life equal to its mana value.

How it works : Illumination

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Illumination.

Netherese Puzzle-Ward

Focus Beam — At the beginning of your upkeep, roll a d4. Scry X, where X is the result. Perfect Illumination — Whenever you roll a die's highest natural result, draw a card.