For decades scholars have investigated the role of amicus curiae briefs in Supreme Court decision-making. Existing work on the influence of these briefs on opinion content focuses exclusively on the use of “borrowed language” where the justices take language directly from the briefs and incorporate it into their majority opinions. Most of the time justices borrow language without attribution. However, much less often, they decide to formally cite the amici. This presents an interesting puzzle; why do justices sometimes borrow language without attribution while at other times they explicitly cite amici while using little of their language?

In this dissertation I argue that borrowing language from an amicus brief and citing it are two distinct uses, done for different reasons, with different implications. Borrowing language is unique in that it is discreet in nature and is unlikely to be revealed to the reader. Therefore, the justices have leeway when it comes to borrowing language as there should be limited influence on perceptions of the Court and its decisions (i.e. the Court’s legitimacy). Citing amicus curiae briefs, however, is much different in that it is clearly revealed to the reader. As such, there can be implications for the Court’s legitimacy depending on what types of interests the justices cite.

I test the implications of this theory using data on over 1,600 cases where amicus briefs were filed in the 1988-2008 terms. I find that the justices borrow language when they need information, and they borrow from ideologically congruent actors. I also find that the evidence on whether they deliberately avoid citing ideologically extreme interests is mixed. On the one hand, they cite less frequently and are less likely to cite in salient cases, but they do still cite ideologically overt interests. Finally, I implement a survey experiment using a high quality, census balanced sample of 3,000 respondents to test whether citations can influence acceptance of Supreme Court decisions. I find that the public is less accepting of citations to ideologically extreme interests and that they are less accepting of decisions that cite interests that are ideologically incompatible with their own preferences.