  Molecular Cloud Complexes (MCCs) are highly structured and ``turbulent''.
Observational evidence suggests that MCCs are dynamically dominated systems,
rather than quasi-equilibrium entities. The observed structure is more likely a
consequence of the formation process rather than something that is imprinted
after the formation of the MCC. Converging flows provide a natural mechanism to
generate MCC structure. We present a detailed numerical analysis of this
scenario. Our study addresses the evolution of a MCC from its birth in
colliding atomic hydrogen flows up until the point when H$_2$ may begin to
form. A combination of dynamical and thermal instabilities breaks up coherent
flows efficiently, seeding the small-scale non-linear density perturbations
necessary for local gravitational collapse and thus allowing (close to)
instantaneous star formation. Many observed properties of MCCs come as a
natural consequence of this formation scenario. Since converging flows are
omnipresent in the ISM, we discuss the general applicability of this mechanism,
from local star formation regions to galaxy mergers.
