The main purpose of this dissertation is to assess ontological issues of information acquisition, focusing on information overload from an integrative perspective of two theoretical foundations, which links two perspectives of consumer behavior in information acquisition: foraging theory in behavioral ecology and information processing theory in marketing. Applying to the integrative investigation, the current research primarily emphasizes the infusion of ecological rationality (i.e., Darwinian Theory) into normative rationality (i.e., Newtonian Theory), but it is not alternative but complementary to each other. Ecological rationality, which is rooted in Darwinism, emphasizes that human behavior has developed through adaptation and natural selection as the human minds interact with environments. The current study consists of five chapters: the philosophical foundation of the rationalities, exploratory study, proposed hypotheses, empirical tests, and general discussion. A summary of the contents of each chapter is: The first chapter aims to provide an integrative framework of consumer information acquisition in order to explore ontological issues in information overload paradigm, attempting to synthesize different approaches in marketing and behavioral ecology. To explore, the current study emphasizes an integrative perspective between two theories for information acquisition (foraging and information processing), which are based on different philosophical foundations of the rationality (ecological and normative). Along with the process of the information acquisition, this study provides relevant consequences (decision-related responses and decision-related alternatives) after the information acquisition process and influential factors in temporal and psychological dimensions (time and motivation). Then, the conceptual study provides conclusion and the current research scope. The second chapter aims to examine the efficacy of the current study's theoretical integration in the process of consumer information foraging so as to approach an ontological issue in information overload paradigm: more information is better vs. less information is better (i.e., information processing theory and foraging theory under an information overload paradigm). Therefore, this study explores and examines what can be appropriate information structures to describe the ontological issue in the process of consumer information foraging. To formulate the adequate information structure, this study attempts to utilize an integrative perspective between marketing and behavioral ecology. This study examines consumers' online activities sequentially from a broad to detail approach, based on the categories of goods and services. The result, by and large, suggests a necessity of an integrative perspective to view a holistic information structure, including quantity, quality, and environment components. These structural components interactively communicate with minds when shaping the process of the consumer information foraging, which are likely to involve in the degree of information overload. Moreover, results demonstrate rather higher variation of strategic information foraging but emphasize some important communality in the initial stage of information foraging, such as the role of search engine and interpersonal communication. In addition, categories of goods and services affect shaping the pattern of strategic information foraging. Then, the conclusion of the study provides. The third chapter aims to propose a hypothetical model, based on the theoretical backgrounds in Chapter 1 and the findings of the exploratory study in Chapter 2. In addition, the pilot study was conducted to provide a concrete framework of the empirical study by checking the manipulation of holistic information structures. The manipulation of the structures includes the total quantity of information, the quality of information, and environmental information. Those structures measured on several resultant consequences, using the patch concepts (within-patch and between-patch). Controversially, in general, consumers tend to prefer more information rather than less information only when arranged information provides; otherwise, this preference attenuates. This controversial result also has conflicting variations, depending on the types of patches. Overall, the comparison in the within-patch and between-patch through displaying heterogeneous information structures suggests that holistic information structures are a more important factor than the mere quantity or quality of information. The fourth chapter empirically tests the theory-based hypothetical frameworks to assess the ontological issues in information overload paradigm using the integrative perspective of the two information acquisition theories. The findings of the empirical study suggest that the real-world information overload is not simply determined by a single dominant factor (e.g., quantity), but by the interplay of intricately intertwined factors. The factors are the following: information structures (three unarranged and four arranged information structures, including quantity, quality and environment), item categories (durables, nondurables and services), and time constraints (time pressure vs. no time pressure). The interwoven complexity implies that paradigmatic change of perspectives in relation with information overload though integrating two important conceptual factors between domain-specific dependency and universality. Moreover, the information overload begins with the browsing stage of acquiring the necessary information, not with the searching stage, suggesting the view of browsing-searching continuum that underscores the important role of the patch concept. As a whole, the conclusive findings suggest an integrative perspective between Darwinism and Non-Darwinism as a prerequisite of providing a better comprehension of the issues of the information overload paradigm. The fifth chapter is the section of general discussion including major findings, theoretical, methodological and empirical implications, limitations, and conclusive statement. / Business Administration/Marketing