lifetimes, and are disrupted only by the energy injected by massive star formation and evolution, another picture is that molecular clouds are relatively transient objects, with the denser regions representing only turbulent fluctuations of density rather than well-defined gravitationally bound condensations [see e.g. review by @vazquez2007].

These issues have been discussed on global scale, addressing the distribution of clouds and the apportioning of molecular and atomic gas in the Galaxy. They are also very relevant to studies of specific molecular cloud complexes, with one of the best–studied of these being that in Taurus. The structure of the interstellar gas in atomic and molecular form, the stellar population, the issue of star formation rate, and the role of different physical processes have all been the subject of numerous papers focused on the Taurus region, primarily because its proximity [140 pc; @elias1978][^1] allows very detailed studies of the morphology of the gas and the relationship between gas and stars. The sheer volume of the data that have been obtained and the number of analyses that have been carried out preclude giving a complete listing of the references to Taurus, so we will have to be selective rather than comprehensive, recognizing that we 