| ALMA, the most advanced sub-mm/mm telescope, is providing an unprecedented opportunity to characterize planetary birth sites, as sub-mm imaging provides vital information on the distribution of the planet-building material, the dusty gaseous discs orbiting young stars at an age of a few Myr. ALMA's unique resolution and sensitivity have recently revealed that the largest dust-rich discs are characterized by suggestive small-scale sub-structures such as rings and spirals (e.g., the celebrated HL Tau). However, the ubiquity of these sub-structures is challenged by homogeneous disc surveys, which suggest that the bulk of the disc populations is instead made of faint, possibly feature-less, compact discs. The empirical trends emerging from this new wealth of information challenge theoretical interpretations in many ways. In this talk I will describe the latest observational advances obtained by the extreme high-resolution campaigns as well as by the near-complete surveys in different star-forming regions. I will discuss what the currently open questions are and how we plan to address them in the future. |