Increasing greenhouse gas concentration in the atmosphere and the resulting warming of the climate are a great challenge for humanity. Politics has several instruments at hand to tackle this issue, one of them being the trade in emission permits. Based on the economic theory of emission trading the paper examines trading systems in the EU, Australia and the US and possible barriers and challenges in linking them. In combination with the opinions and experiences expressed in nine interviews carried out with experts from different areas, private industry, universities and public administration, a number of conclusions could be drawn. These have to be seen in light of a few basic assumptions the reader is made aware of before the start of the main part. They are presented to underline the viability of the cap-and-trade policy vis-à-vis different views. In the end, it turned out that there are several issues which represent major obstacles to linking the systems analysed. Comparability on multiple levels emerged as the essential problem, but also minor deficiencies within the schemes as such proved to be issues of importance beforehand. As a conclusion, for a direct link to become effective in the future, these barriers would have to be removed by political coordination or even integration, which seems unrealistic at present, despite the economic and social similarities in the regions examined. However, an idea to initiate this process is presented at the end as well as an outlook on the issue of involving emerging and developing countries.