From Bubbles and Filaments to Cores and Disks: Gas Gathering and Growth
  of Structure Leading to the Formation of Stellar Systems
  The study of the development of structures on multiple scales in the cold
interstellar medium has experienced rapid expansion in the past decade, on both
the observational and the theoretical front. Spectral line studies at
(sub-)millimeter wavelengths over a wide range of physical scales have provided
unique probes of the kinematics of dense gas in star-forming regions, and have
been complemented by extensive, high dynamic range dust continuum surveys of
the column density structure of molecular cloud complexes, while dust
polarization maps have highlighted the role of magnetic fields. This has been
accompanied by increasingly sophisticated numerical simulations including new
physics (e.g., supernova driving, cosmic rays, non-ideal magneto-hydrodynamics,
radiation pressure) and new techniques such as zoom-in simulations allowing
multi-scale studies. Taken together, these new data have emphasized the
anisotropic growth of dense structures on all scales, from giant ISM bubbles
driven by stellar feedback on $\sim$50--100 pc scales through parsec-scale
molecular filaments down to $< 0.1$ pc dense cores and $< 1000$ au protostellar
disks. Combining observations and theory, we present a coherent picture for the
formation and evolution of these structures and synthesize a comprehensive
physical scenario for the initial conditions and early stages of star and disk
formation.
