Cost reduction is a recurring mechanic in Dominion. Rather than directly fielding coin, cost-reducers decrease the cost of cards, an effect which becomes more valuable with more buys. Typical cost reduction instructions follow this wording:
- [All cards or some subset of cards] (including cards in players' hands) cost less this turn, but not less than .
 List of cost-reducers
- Bridge - the archetypal cost-reducer
- Quarry - only affects Actions
- Peddler - only reduces its own cost during the Buy phase, depending on how many Actions are in play
- Princess - reduces costs by , but only one copy
- Highway - cantrip
- Bridge Troll - effectively increases costs for opponents with the – token
- Ferry - reduces a single Supply pile's cost by
- Inventor - gains a card costing up to before cost reduction kicks in
- Canal - reduces costs on your turn for the rest of the game
Most cards that reference a specific cost in Workshop can gain any card costing up to ; without cost reduction, this effect is rather weak, but with four Highways in play, a Workshop can gain Provinces. On the other hand, cards that give a scaling effect per cost in of another card (most often trash for benefit cards) will do less well with cost-reducers, as their effect will be diminished, and cards that reference a cheaper card will give no effect if their cost has been reduced to . For examples, trashing a Silver to an Apprentice when you have Princess in play will only draw you one card, and with five Highways in play, Band of Misfits can't do anything.do well with cost-reducers, as most such cards use the specific cost as an upper limit. For example,
Since cost reduction affects cards but not Events, it is less useful for strategies that depend heavily on buying Events.