+Buy
Playing a card that provides +Buy increases the number of cards you are allowed to buy during your buy phase.
+Buy is an essential component of most engine strategies, since engines can take a long time to build; +Buy allows you to acquire engine components more rapidly, thus speeding up the construction of the engine, and once the engine is running it allows you to buy multiple Victory cards at once to make up for the slower start. An easy trap to fall into is that of "overbuilding" an engine in the absence of +Buy: there's no use in building a deck that can regularly generate 
each turn if you can still only buy one Province with it. In some cases, if the +Buy card is rather unwieldy like Herbalist, it is good strategy to wait to buy even a relatively cheap +Buy card until you are close to generating enough 
to benefit from the effect, although you need to avoid waiting too long as well or else you will have to waste on the turn you buy that card.
If you are lacking the deck control to generate large amounts of or to assure having a +Buy card in hand when you do, a +Buy card may not be worth its opportunity cost.
Some cards that give +Buy have it as part of their core function, such as Herbalist; usually the +Buy is the only reason for wanting a Herbalist. In some cases, a card offers +Buy as a feature that synergizes with its core function: Collection offers you a 
reward per card you buy, and gives +Buy to make the reward go farther. Other cards have +Buy merely as an extra vanilla bonus that keeps the card competitive with other cards at the same cost: Worker's Village is a village costing {
with the +Buy as an extra bonus for the 
it costs more than Village.
Cards that give unrestricted +Buy
Cards in italics have been removed.
Terminal
- Dominion: Woodcutter
- Intrigue: Baron, Bridge
- Alchemy: Herbalist
- Prosperity: Goons
- Cornucopia: Horse Traders
- Hinterlands: Nomad Camp, Nomads, Souk
- Dark Ages: Squire, Storeroom
- Guilds: Merchant Guild
- Adventures: Peasant, Messenger, Bridge Troll, Wine Merchant
- Empires: Farmers' Market
- Nocturne: Sacred Grove, Druid, Skulk
- Menagerie: Way of the Monkey
- Allies: Herb Gatherer, Town
Terminal draw
Cantrip
Treasures and other non-terminal stop cards
- Dominion: Festival
- Seaside: Astrolabe
- Prosperity: Tiara, Collection
- Hinterlands: Cauldron
- Dark Ages: Counterfeit
- Guilds: Candlestick Maker
- Empires: Villa, Capital, Charm, Fortune
- Nocturne: Pouch
- Renaissance: Ducat, Spices
- Menagerie: Stockpile
+Buy between other options
- Bauble
- Hamlet
- Pawn can provide +Buy in combination with either +Action, +Card, or +.
- Courtier offers +Buy as one of several choices.
- Scrap offers +Buy as one of several choices.
Other
- Travelling Fair can transfer arbitrary amounts of into +Buy
- Seaway and Teacher can give +Buy to an Action card pile in the Supply.
- League of Shopkeepers can give you +buy when you play a Liaison.
Cards that give restricted +Buy
- Some cards need to trash a card, so they only replace cards
- Some cards are difficult to come by or only exist in very limited numbers:
- Cornucopia: Princess
- Dark Ages: Ruined Market, Sir Martin
- Nocturne: The Forest's Gift
- [Renaissance]]: Fair
- Tactician You can generally get only one extra Buy from it and even to make use of this you need to build your deck in a specific way.
- Some cards only work later during the game when one or more piles have emptied:
- Menagerie: Animal Fair
- City (but only after 2 Supply piles are empty)
- Prosperity:Contraband can prevent you from buying certain desirable cards.
- Some effects need you to to gain specific kinds of cards to get +Buy:
- [Allies]]: Galleria, Band of Nomads
- Black Market does not technically provide +Buy, but it lets you buy an additional card during the Action phase.
Giving back Buys
- Forum and Cavalry give +Buy when gained. Similarly, Villa can be played instantly after being gained and so gives back a Buy.
- Galleria and Band of Nomads can give back Buys upon buying certain cards.
Synergies
