Human intermediation is the central issue for information professionals who have been striving to provide better services in ever-changing environments. This document reports on an empirical study of human intermediation to explore patterns of relationships between user situations and tasks they request of intermediaries using the AskERIC Q&A Service--an Internet-based digital reference service--as an instantiation of human intermediation. The book consists of 10 chapters. An Introduction presents an overview of the nature of the problems addressed, research questions, and the structure of the book. Chapter 2, "What Do We Know about User Behavior in Human Intermediation," presents an extensive review of literature that overviews the topic of this research. Chapter 3, "Search for the Optimal Approach," reviews the general research approaches in conventional information retrieval (IR) and information problem solving (IPS) research. Chapter 4,"Methodology of the Empirical Study," describes the research design and procedure applied in this study. Chapters 5 through 9, "Tasks Requested of Human Intermediaries,""Situational Factors Association with the Use of Human Intermediation,""Reasons for Using the AskERIC Q&A Service,""Evaluation of AskERIC Q&A Service," and "Patterns of Associations between Situational Factors and Tasks Requested of AskERIC Q&A Service," present major findings of this study with some implications for existing models of IR and IPS research. Chapter 5 provides the taxonomy of tasks requested of human intermediaries developed in this research. Chapter 6 reports a finding of key situational factors identified by the study as associated with the use of human intermediation and Chapter 7 presents findings on reasons for using human intermediation. Chapter 8 reports findings concerning users' evaluation of the outcome of human intermediation. Chapter 9 reports findings on associations between situational factors and tasks requested of human intermediaries. Chapter 10 discusses the implications of study findings for practices of information services and system design. Four appendices include forms and additional information on findings. (Contains 209 references.) (AEF)