The Cold Cores project started as part of the baseline core programme of the
Planck satellite, resulting in the publication of the Planck Catalog of Galactic
Cold Clumps with (PGCC) more than 13 000 objects. The sources were selected
based on the signature of cold far-infrared (FIR) dust emission and were thus
believed to represent the earliest stages of the current Galactic star
formation. The Cold Cores project was continued through an open time key
programme on the Herschel satellite, and since then many of the sources have
been studied by in more detail with various space-borne and ground-based
instruments, including FIR-radio interferometry and polarimetry.
We will discuss the properties of the original PGCC catalogue and what
subsequent follow-up studies have revealed about the true nature of these
sources. We present results on the varying degrees of star formation activity
and feedback, as well as the dust evolution from general molecular clouds to the
protostellar cores and HII regions associated with the PGCC sources.