  We present a dynamical theory of complex cooperative projects such as large
engineering design or software development efforts, comprised of concurrent and
interrelated tasks. The model accounts for temporal fluctuations both in task
performance and in the interactions between related tasks. We show that as the
system size increases, so does the average completion time. Also, for fixed
system size, the dynamics of individual project realizations can exhibit large
deviations from the average when fluctuations increase past a threshold,
causing long delays in completion times. This effect is in agreement with
empirical observations, and can be mitigated by arranging projects in a
hierarchical or modular structure.
