There was a time when the idea of competitive commercial space launches and global satellite telecommunications networks belonged exclusively to the realm of science fiction. Science fiction has now become reality. Private corporations and even ordinary civilians can participate in space activities. This is a dramatic change from the days when only States were active in space. In those days, States were only responsible for their own activities in outer space. With the introduction of a new class of participants, private entities, it is unclear who now bears responsibility for such activities. This book explores the question in the modern Space Age by briefly examining the evolution of State responsibility and critically evaluating the prevaling theories in this field to develop a different theory to resolve the issue based on a careful interpretation of Article VI of the 1967 Outer Space Treaty. The analysis should provoke discussion amongst academics and law makers regarding current theories relied upon by States to regulate private activities in outer space and be of interest to those in the commercial space business.