Scientific research increasingly requires international collaboration among scientists. Less is known, however, about the barriers that impede such collaboration. In this pioneering study, more than 9000 scientists from eight societies – the United States, the United Kingdom, India, Italy, Taiwan, Hong Kong, Turkey, and France – were surveyed to gauge scientists’ attitudes and experiences. While most scientists claimed international collaboration was important, their actual participation in such collaborations was much lower. We identified the prevalence rates of three types of barriers (political, logistical, and cultural) based on categories developed from previous work. In addition, we identified nine additional categories of barriers. Key barriers to collaboration that scientists identified included lack of funding for international work, restrictions on material and data sharing, and differences in academic standards. Respondents also complained about bias against scholars from emerging or developing countries. Our study highlights areas where efforts could be made to address policy issues, institutional barriers, and national biases to promote more productive collaboration in the global scientific community.