Thisbook isnotatextbook tobecomeacquainted with thelaws ofnature. An elementaryknowledgeaboutlawsofnature,inparticularthelawsofphysics,is presupposed. Thebookisratherintendedtoprovideaclari?cationofconcepts and properties of the laws of nature. The authors would like to emphasise that this book has been developed ¿ created ¿ as a real teamwork. Although the chapters (and in some cases parts of the chapters) were originally written by one of the two authors, all of them were discussed thoroughly and in detail and have been revised and complemented afterwards. Even if both authors were in agreement on most of the foundational issues discussed in the book, they did not feel it necessary to balance every viewpoint. Thus some individual and personal di?erence or