Today, courses on biophysics are taught in almost all universities in the world, often in separate biophysics departments or divisions. This reflects the enormous growth of the field, even though the problem of its formal definition remains unsettled. In spite of this lack of definition, biophysics, which can be considered as an amalgamation of the biological and the physical sciences, is recognized as a major scientific activity that has led to spectacular developments in biology. It has increased our knowledge of biological systems to such an extent that even industrial and commercial interests are now beginning to put their stamps on biological research. A major part of these developments took place during the last two decades. Therefore, an introductory textbook on biophysics that was published a dozen years ago (c. Sybesma, An Introduction to Biophysics, Academic Press, 1977) no longer could fulfil " ... the need for a comprehensive but elementary textbook ... -" (R. Cammack, Nature 272 (1978), 96). However, because of the increased proliferation of biophysics into higher education, the need for introductory course texts on biophysics is stronger than ever. This fact, together with valuable comments of many readers, have encouraged me to revise the original book.