Infomediaries are information intermediaries in the Internet that play an important part in reducing online customers’ search costs for finding the most suitable vendors and products. This research explores the process of Web customers’ trust building using infomediaries. Specifically, we identify four sets of trust-related beliefs that impact web customers’ trust attitude and intended behavior, as well as the antecedents of trust-related beliefs. This conceptualization is built on a number of theories, mainly theories of trust, reasoned action, and actor-network. Our empirical results in testing the model indicate that web customers’ trust attitude toward web infomediaries is formed based on their beliefs regarding risk, content quality, system quality, and trust- building beliefs. We also found that initial trust is the antecedent of trust-forming beliefs, whereas individuals’ propensity to trust influences their calculative risk beliefs. The implications of these findings are also discussed.