> ## Documentation Index > Fetch the complete documentation index at: https://docs.calibri.io/llms.txt > Use this file to discover all available pages before exploring further. # Core Concepts > Binary YES/NO markets, prices as probabilities, the combined order book, contracts, settlement, and the market lifecycle. Everything on Calibri is built from a few simple ideas. Understand these and the rest of the platform follows. ## Binary YES/NO markets Every market asks one question with exactly two outcomes: **YES** or **NO**. Each market has two contracts: * A **YES contract** pays **1.00 USDC** if the outcome is YES, and **0** if NO. * A **NO contract** pays **1.00 USDC** if the outcome is NO, and **0** if YES. You take a view by buying the side you believe in. Buying YES profits if the event happens; buying NO profits if it doesn't. ## Prices are probabilities A contract's price is always between **0.01 and 0.99**, and it reads directly as the market's estimated probability of that outcome. | YES price | Market is saying… | | - | - | | `0.10` | \~10% chance of YES | | `0.50` | a coin flip | | `0.90` | \~90% chance of YES | Because YES and NO are the two halves of the same question, their prices always sum to **1.00**: ``` YES price + NO price = 1.00 ``` If YES trades at `0.65`, NO is `0.35`. Buying NO at `0.35` takes the opposite view to YES at `0.65` — the two prices are two readings of one question. ## The combined order book Calibri does **not** keep a separate book for NO. There is **one combined order book** per market, priced in YES terms, and the YES+NO=1.00 identity is enforced by construction. This keeps liquidity in one place instead of splitting it across two half-empty books. Because a YES and a NO contract together always pay 1.00, **buying YES at `0.60` is the same trade as selling NO at `0.40`**. So a resting YES bid at `0.60` is also NO on offer at `0.40`. A YES buyer can be filled by someone selling YES **or** by someone buying NO; in the second case a new YES/NO pair is created for the two of them. See [The combined order book](/trading-placing-orders#the-combined-order-book) for all four order kinds and what each match does. ## What a contract is A **contract** is created the moment the engine matches a YES buyer with a NO buyer. Their two payments, which add up to 1.00 USDC, go into the market's escrow: one member holds the YES side, the other holds the NO side, and together their stakes fund the full 1.00 USDC that the winner will eventually collect. Once created, a contract can change hands — a holder can sell it to another buyer — and settlement pays whoever holds the winning side. * Your **position** in a market is the set of contract legs you hold (net YES, net NO, or flat). * You can hold a position to resolution or **sell** it before then. Buying the opposite side does not net against the first — each leg is collateralised independently, so it locks additional capital instead of returning any. ## Settlement — winner takes 1.00, loser takes 0 When a market resolves, each contract pays out: ``` Winning side → 1.00 USDC per share Losing side → 0 ``` The winner collects the **full pot** — their own stake plus the loser's stake. There is **no fee at settlement or redemption**. Your only trading cost is the **taker fee at the time of the fill** (see [Fees](/concepts/fees)). Winners **redeem on-chain** themselves — resolution makes the winning outcome token redeemable for 1.00 USDC per share, and you claim it. See [Redeeming winnings](/non-custodial/redeeming-winnings). ## Market lifecycle From a trader's point of view, a market moves through these stages: The market is live. You can place, fill, and cancel orders; prices move as people trade. Trading stops at the market's close time. Open orders stop matching and your positions are locked in, pending the outcome. Closing is not the same as answering. Where the outcome only becomes knowable some time after close, the market states an **answer deadline** up front — see [Market resolution](/non-custodial/resolution). The outcome is determined and contracts pay out — winners 1.00/share, losers 0\. This is the normal end state. If a market can't be resolved fairly, it is **voided**: every share pays 0.50, YES and NO alike, and the taker fee is returned. That is not a refund of what you paid — see [Voids and postponements](/non-custodial/resolution#voids-and-postponements). The four stages above are the summary; the API reports finer-grained statuses within them. Resolution runs on-chain through an escalation ladder — see [Market resolution](/non-custodial/resolution). ## Putting it together | Concept | Key idea | | - | - | | **Binary market** | One question, two outcomes: YES / NO | | **Price** | Reads as probability; YES + NO = 1.00 | | **Order book** | One combined book; buying YES at `p` = selling NO at `1.00 − p` | | **Contract** | Jointly owned YES/NO pair funding a 1.00 payout | | **Settlement** | Winner 1.00/share, loser 0, no settlement fee | | **Lifecycle** | Open → Closed → Resolved (or Voided) | ## Related The single taker fee, charged once at the trade. Maker rebates and referral rewards. Series, windows, and price-feed markets. The data source behind each market type. Placing a signed limit order in practice. Market, order-book, and ticker endpoints. 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