This is the first monograph on computation in living cells - one of the central and fastest growing areas of research in this field. Gene assembly in ciliates (unicellular organisms) is a splendid example of such computations. This work has helped to clarify important biological aspects of gene assembly, yielded novel insights into the nature of computation, and broadened our understanding of what computation is about. The monograph gives an accessible account of both the biology and the formal analysis of the gene assembly process. It can be used as a textbook for either graduate courses or seminars.