So farTheorygame, this book has been devoted to formulating and solving problems in which a single decision-maker acted for himself/herself, and the values of the objective functionFunctionobjective have been clearly given. In everyday life, however, people often encounter tasks where they have to decide between several options, even though they do not know the exact consequences of their decisionDecision. Various random variablesVariablesrandom can affect this result (e.g., you are planning a birthday party and do not know how much food and drinks to buy because you cannot estimate which of the invited people will get sick and which will refuse to come for other reasons). In some cases, it is possible to estimate the approximate probabilityProbability that a given result will occur (e.g., you know the weather forecast when planning a weekend trip with the family); however, the consequence of a given decisionDecision is completely random sometimes (e.g., which lottery ticket to buy from the offered pieces). A different type of problem occurs when another “intelligent” participant, typically a person or persons, enters the decision-making process. This type of decision-making process is called a gameGame in this chapter. You can either compete with this other participant(s) or cooperate with him/her/them to achieve the greatest possible common benefit.