Schematic picture of molecular cloud structure over spatial scales from >10 pc to ~0.1 pc: from cloud to core scale. A molecular cloud starts contraction from an initial stage that appears to be an infrared dark cloud (IRDC) and evolves into a star-forming one, embedding a number of molecular clumps. The massive clumps, ~1 pc in size, are generally composed of filamentary structures and cores at different evolutionary stages. In all figures, the yellow curved arrows represent turbulent motions and the purple arrows indicate gravitational contractionor gas inflows (along filaments). In the rightmost figure, the thick lines show filaments and the blue ovals indicate cores of different masses; the color gradient of the clump indicates a density gradient of the bulk gas. The characteristics of different structures are linked to textboxes by dotted arrows.