What compose organisms at any given time are bonded things that are able to form fresh bonds to new things and to break bonds that are already in place. The activities of their constituents are organized and controlled, or integrated, under the guidance of information they carry. This is a very rough picture of what composes organisms. After sketching it out, I considered three ways of refining it – three accounts of the composition of an organism at a time and over time. The first, the gradualist account, says that an organism survives only incremental changes that leave its constituents integrated. However, organisms may survive grave injuries and radical forms of surgery that change their composition suddenly and dramatically. The second, unrefined integratist account, solves this problem, as it allows for even drastic changes in an organism’s constituents, as long as these leave them capable of activities integrated in conformity with the information that was encoded in the nucleic acid within them before the change. But the unrefined account implied that an organism could become two, and two one. To solve that problem I offer a third account, integratism, which says that an organism’s constituents can only undergo nondiverging, nonmerging replacements.