This report draws upon two data sets to examine the gender wage gap among member institutions of the Association of Research Libraries (ARL). The first data set consists of 35 years of salary survey data collected by ARL and is used to provide trend data on the gender wage gap from 1980 to 2014 as well as present an in-depth look at the wage gap in 2014. After controlling for variables such as years of experience, position, and type of library in the 2014 ARL Salary Survey data, results revealed that women on average made approximately 2 percent less than their male counterparts in 2014. The second data set comes from a survey of ARL institutions conducted by the researchers in 2015 and is used to explore the influence of additional variables on the gender wage gap that were not found in the ARL Salary Survey data. Results from both data sets suggest a substantial difference between the gender wage gap in ARL institutions and the workforce as a whole.