This dissertation tests a new account of rapid word learning and vocabulary growth that these processes develop as the result of attentional biases to the features of a category that are relevant to labeling/categorization, built as the result of word-learning experience within each category. Study 1 demonstrated that children's vocabulary size within a category predicts their ability to learn new words within that category. Study 2 demonstrated that training children in different numbers of words in two categories leads to differences in their word-learning ability in those categories. Finally, Study 3 demonstrated that children build their vocabularies in the real world in ways that are predicted by the account. Taken together, the results of these studies provide preliminary support for the account, and carry implications for our understanding of word-learning behavior and language-acquisition phenomena. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]