This dissertation explores the effects of frequency on the learning and use of linguistic constructions. The work examines the influence of frequency on form choice in production and meaning inference in comprehension and discusses the effect of each modality on diachronic patterns of change in language. In production, high frequency of a form increases its accessibility given its meaning, and other related meanings. Under the pressures of online real-time speech production, greater accessibility makes a frequent form more likely to be selected over its competitors. Consequently, frequent forms are extended to novel meanings in production, resulting in a synchronic correlation between frequency and polysemy. At the same time, frequency in comprehension results in entrenchment--the more often a form is experienced with a meaning, the more confident the learner becomes that the form is unlikely to be used to express other meanings. The findings reconcile two seemingly contradictory effects of frequency in language change and language acquisition. While frequency results in extension of a frequent form to other meanings in production, it can, at the same time, cause entrenchment in comprehension, which curbs over-extension. The struggle between the pressures from production to extend and from comprehension to entrench molds language. I further provide experimental evidence demonstrating that frequent forms push their infrequent competitors out of their shared meanings, and that infrequent forms competing with frequent forms tend to be assigned to novel related meanings in comprehension. This result suggests a mechanism for the survival of infrequent forms in specific niches and the existence of push chains in semantic change. This dissertation includes previously published co-authored material. [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.]