Guided by the theoretical frameworks of interactive information searching and user engagement (UE), this dissertation employs a three-phase study to conceptualize UE in visual interactive information searching by exploring its conceptual dimensions, examining its measurements, and investigating the relationship between UE, search tasks, and information systems. Using a mixed-methods approach based on a survey, the phase I study validates the applicability of an existing UE scale in the context of visual information searching; finds that a latent cognitive element, sense discovery, can be an UE attribute; and suggests that an improved 46-items scale can be employed to measure the UE attributes. The phase II and phase III studies employ experimental approaches to examine the dimensions of UE concept and the relationship between UE, task characteristics, and information systems. It is found that UE is strongly affected by task type regarding task goal, information media (i.e., image, video, and text), and users’ perception of search tasks, such as task difficulty and complexity, task familiarity and interest, the familiarity and interest in task topic, definition certainty of the concepts in search tasks, and the specific degree of information needed. In the meantime, users’ perception of search tasks can mediate the relationship between their psychological involvement and search actions. In addition, users’ satisfaction with information search results and information systems are both affected by users’ engagement in visual information searching.