Infect is a keyword ability that was introduced in Scars of Mirrodin.   It is centered in black and green with some artifacts having the keyword. It combines poisonous and wither abilities. In Mirrodin Besieged the mechanic was expanded to white. 
As with its related mechanic proliferate, infect is Phyrexian in theme. Each creature with infect, and all cards that gave infect and/or positively affected creatures with infect, were printed with the Phyrexian watermark.
- Infect's effect applies to any damage, not just combat damage.
- The -1/-1 counters remain on the creature indefinitely. They're not removed if the creature regenerates or the turn ends.
- Damage from a source with infect is damage in all respects. If the source with infect also has lifelink, damage dealt by that source also causes its controller to gain that much life. Damage from a source with infect can be prevented or redirected. Abilities that trigger on damage being dealt will trigger if a source with infect deals damage, if appropriate.
- If damage from a source with infect that would be dealt to a player is prevented, that player doesn't get poison counters. If damage from a source with infect that would be dealt to a creature is prevented, that creature doesn't get -1/-1 counters.
- Damage from a source with infect affects planeswalkers normally.
 Reminder text
The latest reminder text for Infect reads "This deals damage to creatures in the form of -1/-1 counters and players in the form of poison counters.".
 Color percentages
 Cards that grant just Infect
 Cards with Infect
- Infect was featured as rules card 1 of 5 in the Scars of Mirrodin set and as rules card 4 of 5 in the Mirrodin Besieged set and as rules card 3 of 4 in the New Phyrexia set.
- Mark Rosewater. (September 06, 2010.) "Something Wicked This Way Comes, Part 1", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Tom LaPille. (November 05, 2010.) "Infection Spreads", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Mark Rosewater. (January 24, 2011.) "Under Besiege, Part 2", Daily MTG, magicthegathering.com, Wizards of the Coast.