The availability of information in different languages on the Internet allows multilingual web users to search in multiple languages for the same search task. When web users can search in multiple languages, they may combine these languages in various ways during searching. Few studies have examined multilingual web users' code-switching search behaviors in two or more languages online. This work bridges this gap, aiming to investigate the factors that impact code-switching search behaviors of native Chinese web users who speak English as their second or foreign language (L2 users) and explore the L2 web users' code-switching search patterns and strategies when they seek information online. This dissertation consists of two phases. The Phase I study confirms that code-switching search behaviors naturally occur when L2 web users search for information online by using the methods of diaries and interviews. Findings highlight that code-switching occurred in a wide range of search topics in L2 web users' daily searching. The factors, such as language proficiency and translation, information sufficiency, cultural preferences, and feelings and attitudes, impacted L2 web users' situational and metaphorical code-switching search behaviors. In the Phase II study, controlled lab experiments and follow-up interviews were conducted so as to study L2 web users' code-switching information seeking behaviors in more detail during searching. This in-depth study revealed the L2 web users' code-switching search models, strategies, and more factors such as context, information verification, language image, and website credibility that impacted their code-switching behaviors. The purpose of this work is to describe code-switching search behaviors and to provide design implications for multilingual search systems. It contributes to a detailed study of L2 web users' language selection search behaviors from an interdisciplinary perspective using sociolinguistics and information technology. [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.]