Bridge bidding systems that incorporate a strong 2 clubs opening bid include modern Standard American, standard Acol, 2/1 game forcing and many others. In most natural bridge bidding systems, the opening bid of 2♣ is used exclusively for hands too strong for an opening bid at the one-level. Typically, the bid is reserved for hands that are almost strong enough to bid to the game level on their own power, or even stronger. The exact requirements for the bid vary considerably depending upon the system used and partnership agreement.