  The cycling of material from the interstellar medium (ISM) into stars and the
return of stellar ejecta into the ISM is the engine that drives the "galactic
ecology" in normal spirals, a cornerstone in the formation and evolution of
galaxies through cosmic time. Major observational and theoretical challenges
need to be addressed in determining the processes responsible for converting
the low-density ISM into dense molecular clouds, forming dense filaments and
clumps, fragmenting them into stars, OB associations and bound clusters, and
characterizing the feedback that limits the rate and efficiency of star
formation. This formidable task can be now effectively attacked thanks to the
combination of new global-scale surveys of the Milky Way Galactic Plane from
infrared to radio wavelengths, offering the possibility of bridging the gap
between local and extragalactic star formation studies. The Herschel, Spitzer
and WISE mid to far infrared continuum surveys, complemented by analogue
surveys from ground-based facilities in the millimetre and radio wavelengths,
enables us to measure the Galactic distribution and physical properties of dust
on all scales and in all components of the ISM from diffuse clouds to
filamentary complexes and tens of thousands of dense clumps. A complementary
suite of spectroscopic surveys in various atomic and molecular tracers is
providing the chemical fingerprinting of dense clumps and filaments, as well as
essential kinematic information to derive distances and thus transform
panoramic data into a 3D representation. The latest results emerging from these
Galaxy-scale surveys are reviewed. New insights into cloud formation and
evolution, filaments and their relationship to channeling gas onto
gravitationally-bound clumps, the properties of these clumps, density
thresholds for gravitational collapse, and star and cluster formation rates are
discussed.

Astrophysics of Galaxies