Complicating matters further, all of these regulations differ between different national or regional authorities, leading to manufacturing inefficiencies, regulatory incompatibilities and ethical dilemmas that obstruct progress in the field. For example, whether a PSC line can be used for therapy varies in different countries depending on when consent is obtained, whether consent allows research or clinical use of samples, and what withdrawal of consent means. There are differences in the rules covering the use of serum; a serum-exposed product manufactured in the United Kingdom cannot be imported into the United States. ESC lines cannot be patented in Europe or in Korea but can be patented in the United States. Human genetic material cannot be shipped out of India, and it is very difficult to obtain ESCs from Japan. Conflicting regulations limit the use of banked PSC lines to particular countries or patients, or, in many cases, to no one. PSC-based therapies are being developed to treat a broad range of diseases, and the regenerative medicine community must strive to provide the therapies efficiently in as many countries as possible. Ongoing efforts by regulators and others to address these issues, while commendable, lack coordination. We urge all stakeholders to work together to build a consensus strategy that enables harmonization and appropriate prioritization of tasks. This letter, signed by members of several public and private organizations in the field, represents a first step toward building such a consensus. We propose a set of issues that should be addressed, divided into those that are within (Box 1) and