Human word learning is remarkable: We not only learn thousands of words but also form organized semantic networks in which words are interconnected according to meaningful links, such as those between "apple," "juicy," and "pear." These links play key roles in our abilities to use language. How do words become integrated into our semantic networks? Here, we investigated whether humans integrate new words by harnessing simple statistical regularities of word use in language, including: (a) Direct co-occurrence (e.g., "eat-apple") and (b) Shared co-occurrence (e.g., "apple" and "pear" both co-occur with "eat"). In four reported experiments (N = 139), semantic priming (Experiments 1-3) and eye-tracking (Experiment 4) paradigms revealed that new words became linked to familiar words following exposure to sentences in which they either directly co-occurred, or shared co-occurrence. This finding highlights a potentially key role for co-occurrence in building organized word knowledge that is fundamental to our unique fluency with language.