This issue ofPHYSICS TODAYis devoted to the interface between physics and biology, commonly termed biological physics or biophysics. Physicists tend to consider biological physics as physics inspired by biology and biophysics as biology revealed by physical methods—or to put it colloquially, what biology can do for physics and what physics can do for biology. Biologists take a broader view. Cells and organisms must know some physics as well as biology because they have evolved in the face of daunting physical constraints. So biophysics includes the physics mastered by living things. Some of this physics is understood by physicists, and some is not. In the former case, one is awed by how much physics organisms know. In the latter case, one is intrigued by how much physics they might yet reveal. The topics addressed in this issue ofPHYSICS TODAYdeal with these two domains.