The main purpose of this session is to gather observational data which should ultimately yield a better understanding of the relationships between the interstellar matter and the stars in our Galaxy. Ideally we would like to know how the Galaxy evolves in this respect and in particular to understand quantitatively the laws of star formation: What is the relation between star formation and the density of gas? (for a study of this kind see Guibert, Lequeux, and Viallefond, Astron. Astrophys. 68, 1, where Schmidt's law is rediscussed); Does the Initial Mass Function (IMF) vary within the Galaxy? (for recent studies see Burki, Astron. Astrophys. 57, 135, and Puget, Serra, and Ryter, this Symposium). We are obviously still far from being able to give definitive answers to these questions, but I hope that we will obtain at least a better understanding of the basic ingredients: the distribution of interstellar matter and of young stars.