Modular system for composing footwear assembled by combining at least two interchangeable modules connected in a removable way by connection means, said interchangeable modules comprising: - a sole module (5, 13) removably connectable to an upper module (6, 14) and comprising a sole of elastic material (85, 86), along the edge (91, 92) of which a joining module is a fixed upper sole (97, 98) comprising connection means between the modules for removably connecting the sole module (5, 13) to the upper module (6, 14), - the upper module (6, 14) removably connectable to the sole module (5, 13) and connectable to upper modules by means of connection means connected to its edge (59, 60, 63, 64), - a tab module removably connectable to the upper module (6, 14) by means of connection means connected to lateral sections (117, 120) of the tab module and to the upper part of the upper module (6, 14), - an ankle-cutting adapter module (17, 18, 21, 23, 25, 27) removably connectable to the upper module (6, 14) and to upper modules by means of connection means connected to the lower and upper edges and/or to the vertical sides, - a boot module (30, 32, 34, 36, 38, 40, 42, 44) removably connectable to the corresponding ankle size adapter module (17, 18, 21, 23, 25, 27) and to the upper modules by means of connection means connected to the lower and upper edges and/or to the vertical sides, - a thigh size adapter module (46, 48, 51, 53) removably connectable to the corresponding boot module and to the upper modules by means of connection means connected to the lower and upper edges and/or to the vertical sides, - a finishing module (7, 15, 19, 20, 22, 24, 26, 28, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 52, 54) removably connectable to the corresponding lower modules by means of connection means to the lower edge. - a sole module (5, 13) removably connectable to an upper module (6, 14) and comprising a sole of elastic material (85, 86), along the edge (91, 92) of which a joining module is a fixed upper sole (97, 98) comprising connection means between the modules for removably connecting the sole module (5, 13) to the upper module (6, 14), - the upper module (6, 14) removably connectable to the sole module (5, 13) and connectable to upper modules by means of connection means connected to its edge (59, 60, 63, 64), - a tab module removably connectable to the upper module (6, 14) by means of connection means connected to lateral sections (117, 120) of the tab module and to the upper part of the upper module (6, 14), - an ankle-cutting adapter module (17, 18, 21, 23, 25, 27) removably connectable to the upper module (6, 14) and to upper modules by means of connection means connected to the lower and upper edges and/or to the vertical sides, - a boot module (30, 32, 34, 36, 38, 40, 42, 44) removably connectable to the corresponding ankle size adapter module (17, 18, 21, 23, 25, 27) and to the upper modules by means of connection means connected to the lower and upper edges and/or to the vertical sides, - a thigh size adapter module (46, 48, 51, 53) removably connectable to the corresponding boot module and to the upper modules by means of connection means connected to the lower and upper edges and/or to the vertical sides, - a finishing module (7, 15, 19, 20, 22, 24, 26, 28, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 52, 54) removably connectable to the corresponding lower modules by means of connection means to the lower edge.