This document summarizes a conceptual model exploring the relationship between ethnic diversity/immigration and social capital, and the potential mediating role of nationalism. It hypothesizes that countries with high levels of civic nationalism will experience a smaller negative effect of diversity on social capital than countries with high levels of ethnic nationalism. The document outlines the variables that will be used, including measures of nationalism, social capital, and diversity/immigration drawn from different datasets. It also notes some control variables that will be included like levels of democracy, inequality, and institutional effectiveness.