Physics has always influenced other fields, from the mirrors of Archimedes which were supposed to ignite the sails of enemy warships, to the hydrogen bombs which could destroy Sao Paulo and Dusseldorf. More recently, (com­ putational) statistical physics has been applied to biology, economics, world politics, etc. This book presents some examples in this direction to explain these methods. We do not claim to present a textbook of biology, or a so­ lution of economic problems; we merely explain how physicists like us did it, in order to encourage others to try similar interdisciplinary work. The theo­ ries presented here may not be the best ones for the problems but should be the ones closest to statistical physics methods. In most fields we give only the general idea to guide the reader to the original literature; for the Penna model of biological ageing we try to give a more complete overview, including computer programs, so that readers can start their own research immediately in this field. The selection of material follows our own experience, and even with these selected applications we would appreciate if readers would inform us about overlooked literature. We prove our ignorance, if we do not cite impor­ tant papers. We thank many people, in particular M. Azbel, A. T. Bernardes, S. Dasgupta, S. Galam, H. J. Herrmann, N. Jan, H. Milbrodt, T. J. P. Penna, S. Solomon, D. Sornette, Y. C. Zhang and R.