Economists use various trade dependence indexes as an aggregate measure for comparing across countries the importance of trade and the influence of trade policy. Two commonly used indexes, the trade/GDP index and the export/GDP index, lack mathematical attributes necessary to accurately represent trade dependence. A new index developed in this report, the "trade dependence index" (TDI), should better serve the needs of trade researchers. The TDI unambiguously specifies a country's trade dependence on a scale between zero and 100. Moreover, for any degree of trade dependence there is only one index value.