# Core Concepts

• In the Balancer v3 architecture Routers serve as the pivotal interface for users (not the Vault)
  • Single swaps: Balancer Router
  • Multi-hop swaps: Batch Router
• Sender should use Permit2 to approve the Router to spend each swap input token
• Token amount inputs/outputs are always in the raw token scale, e.g. 1 USDC should be sent as 1000000 because it has 6 decimals
• There are two different swap kinds:
  • ExactIn: Where the user provides an exact input token amount.
  • ExactOut: Where the user provides an exact output token amount.
• There are two subsets of a swap:
  • Single Swap: A swap, tokenIn > tokenOut, using a single pool. This is the most gas efficient option for a swap of this kind.
  • Multi-path Swaps: Swaps involving multiple paths but all executed in the same transaction. Each path can have its own (or the same) tokenIn/tokenOut.
• Boosted Pools and Liquidity Buffers enable gas effective swaps through capital efficient pools (see Boosted Pool section)
• Balancer v2 used the concept of poolIds, this is no longer used in v3 which always uses pool address
• Balancers new API can be used to access pool data