Herschel and Planck are very complementary in the study of pre-stellar cloud cores and of star formation. Planck satellite has covered the entire sky, with good sensitivity but only modest spatial resolution. Being the largest space telescope so far, Herschel is able to take images that have much higher resolution. For our studies, Planck pinpoints the most interesting targets on the sky. These are then mapped with Herschel in order to get a more detailed picture of the structure of the star forming regions, the clouds and the dense cores that may already be collapsing under gravity. Compared to Planck, Herschel covers also some shorter wavelengths, down to 100µm and below. The combined data help to separate the cold cloud cores from the warmer surrounding clouds, to estimate the density and temperature of the various cloud structures, look at variations in the properties of interstellar dust grains, and to catalogue both pre-stallar cores and cores that are already heated by young stars.