Living matter obeys the laws of physics, and the principles and methods of theoretical physics ought to find useful application in many areas of biology. This truism is becoming ever more relevant with the rapid growth of the ability of biological experiments to produce comprehensive quantitative data. After a broad survey of the theoretical questions that today's biology is bringing to the fore, I will tell you about my own attempts to deal with some of them, with a focus on cellular biology. I hope to convince you that theoretical physics and biology have much to offer each other, and that relations between them are destined to grow closer over time. I am certain that I can convince you that a good time will be had by all.