My dissertation consists of three chapters and I take different approach in each chapter to investigate economic decision making behavior. The first chapter analyzes individuals' strategic decisionmaking when players have replaceable identities and private information in a repeated prisoner's dillmma game. The second chapter studies individuals' non-strategic decision making when she has incomplete information about her underlying preference in a sequential choice situation. The third chapter experimentally examines a link between an individual's strategic thinking and nonstrategic decision making in a setting designed to elicit beliefs about independent random variables. In the first chapter, I focus on strategic decision making of economic agents when they are replaceable in a repeated prisoners dilemma. I assume that agents have different private information that restricts their set of actions, and that replacement of agent involves change of such private information. In this environment, some agents are required to signal their own private information to induce their opponents cooperative response, which may induce Pareto improvement of their expected continuation payoffs. Except for a trivial equilibrium, we can have non-trivial equilibria supporting cooperative action as a part of the equilibrium play; however, different from the environment with two long-run agents, replaceable agents environment puts a restriction on an existence of the equilibrium in which agents share the risk of type uncertainty equally regardless of the past history. Because of replacement, agents can avoid a full cost of signaling by shifting it to their successor upon their own replacement. As replacement incurs such a situation with a strictly positive probability, the equilibrium cannot avoid failure. In the second chapter I focus on an economic agent's optimal decision making in a non-strategic environment. Especially, I study a sequential choice problem where an agent's preferences evolve over time. I assume that an agent has an underlying preference, and she learns about her underlying preference depending on her choice histories. Given that an agent makes an optimal decision upon her current available menu, I characterize the sequential choice behavior that follows a Sequential Weak Axiom of Revealed Preference (WARP-S). Using this characterization, I provide criteria for sequential choice data that recovers agents underlying preference. In the third chapter I and my co-author, Duk-Gyoo Kim, focus on a link between an optimal decision making in a non-strategic environment and strategic environment. Our research investigates whether an individual decision maker follows own subjective optimization in a non-strategic decision making, and such a difference in subjective optimization is correlated with strategic decision making pattern. We conducted two separate sessions in the same subject. Each session is designed to identify subjects' behavioral pattern in strategic and non-strategic decision making environment respectively. From the data, we observed that subjects behavioral pattern shows significant similarity in two sessions.