This dissertation examines the effects of issue frames and individual-level mediating factors on attitudes toward same-sex marriage and civil unions. It employs three survey experiments to test both competing and non-competing frame environments, an advance which will clarify the effect of these environments on public opinion. Prior literature on multiple frame environments has failed to reach consensus on the effects of multiple frame environments (MFEs) on public opinion, MFEs may: moderate subject opinion or facilitate stronger connections between subject core values and issue opinions. Results indicate that frame effects vary with framing environment: subjects presented with two persuasive frames advocating the same issue position, or a persuasive frame advocating one position and an unpersuasive frame advocating another, reported opinions closer to the persuasive frames than the control groups. Subjects who received persuasive frames advocating contrary positions reported more moderate positions than the control groups. The magnitude of frame effects also varied by question, with larger effects recorded for the civil unions question than the same-sex marriage question. On balance, these findings support the literature suggesting that multiple frame environments moderate public opinion, although some core value-issue opinion linkages were strengthened by the framed environments. Results for the individual-level political sophistication hypotheses were inconclusive. This thesis extends prior work on MFEs to a salient and divisive issue, with multiple possible solutions. In doing so, it helps resolve a debate in the literature on the effect of MFEs on public opinion. It also provides a first test of individual-level factors, such as respondent political sophistication, which may mediate the reception and processing of these frames by citizens. Finally, this thesis tries to bring both of these literatures into communication with one another to better understand the effects of each in relation to public opinion.