Both intercalated and exfoliated poly(L,L-lactide) (P(L,L-LA)/ organomodified montmorillonite nanocomposites were synthesized by in situ ring-opening polymerization of L,L-lactide, in bulk, directly in the presence of the nanofiller. Intercalation of polyester chains was found to appear even for natural unmodified montmorillonite-Na+, while exfoliation occurred when the aluminosilicate layers were modified by ammonium cations bearing primary hydroxyl groups. Clay delamination was effectively triggered by the grafting reaction of the growing PLA chains onto the hydroxyl groups. Aluminium triisopropoxide, triethylaluminium, and stannous octoate, as initiating or co-initiating species, were compared in terms of polymerization control. The influence of nanoclay content (from 1 to 10 wt.-% in inorganics) on morphology and thermal behavior was also studied. In parallel, a highly filled nanocomposite (called master-batch), prepared by in situ polymerization, was dispersed into a (plasticized) preformed polylactide matrix in the molten state, to reach a better clay delamination than that obtained by direct melt blending. Finally, L,L-Iactide and α,co-dihydroxylated poly(elhylcne glycol) (PEG 1000) were copolymerized in presence of clay in order to study the behavior of the resulting triblocks towards nanocomposite formation.