Since 2016, Joint External Evaluations (JEEs) help countries assess their health security preparedness and capacity to respond to public health risks. JEEs are 1 of 4 components of the International Health Regulations 2005 (IHR) Monitoring and Evaluation Framework. Compared with the mandatory State Party Self-Assessment Annual Reporting tool, JEEs use a transparent, rigorous, and collaborative process with international and in-country experts to evaluate IHR implementation. Because it is voluntary and not all States Parties have completed JEEs, we conducted a multiple linear regression model using publicly available JEE data to estimate global IHR implementation. We extracted JEE scores from the published JEE reports for 78 States Parties to the IHR and 12 sociodemographic, economic, and health indicator variables from 3 official reports and 3 official databases for all 194 World Health Organization Member States. Our final model consisted of 4 variables that significantly account for the variance of JEE score: total score from IHR annual reporting, lost disability-adjusted life years due to communicable diseases, gross domestic product, and health professional density (adjusted R2 = 0.833; P < .0001). We estimated only 1 in 10 countries (n = 19, 9.7%) worldwide had achieved average scores indicating demonstrated capacity or sustainable capacity across the 19 technical areas in the JEE tool. All 19 of these countries were in the high-income group, according to the World Bank classification, and were ranked very high on the Human Development Index, according to the United Nations Development Programme. These findings highlight the importance of ongoing efforts toward advancing global health security, especially in middle- to lower-income countries with limited resources.