A system for the preparation of beverages including capsules (C) with a cup-shaped body (1) having an annular lateral wall (6) which tapers from a mouth opening (2) towards a bottom wall (5). These capsules (C) are of at least a first type and a second type, and have identical bottom walls (5) and different axial lengths (h1, h2, h3). An infusion assembly (10) has a variable-volume infusion chamber (20), having an introduction opening (20a), an end delimitation part (16a) having a shape corresponding to that of the bottom wall (5) of the capsules (C), and with a lateral delimitation structure (13a, 13b; 14) which includes a static portion (13a, 13b) and which extends between said introduction opening (20a) and the end delimitation part (16a). The latter is movable away from the introduction opening (20a).