Nanobiotechnology is still a developing field. The results and promises of this technology are not only of scientific and economic importance, they also raise grave ethical, legal, and social questions. In this context, the so called "Precautionary Principle" or "Vorsorgeprinzip" is of high relevance. What does it mean to "proceed with caution" in the field of nanobiotechnology? How can the principle be applied and specified? Is it a suitable tool for the protection against potentially dangerous effects on the environment and human health? What is the status of the Precautionary Principle in international agreements and national legislation? "Proceed with Caution?" examines the questions that surround the Precautionary Principle in nanobiotechnology. (Series: Munster Studies on Bioethics / Munsteraner Bioethik-Studien - Vol. 12)