Invited review abstract

In this review I will discuss molecular clouds as the mass reservoir for star formation in our Galaxy, focusing on their spatial and kinematic structure and on physical conditions that promote or inhibit star formation. As molecular clouds mark the transitional phase between continuous (nebulous) and discrete (core/stellar) structures, methods developed to analyse them have similarly incorporated both continuous and discrete aspects. I will review the advantages and disadvantages of these two complementary approaches and identify directions needed for future research.