A guide system for guiding a furniture door, in particular a folding door or a folding-sliding door, relative to a stationary furniture part, comprising at least one first guide rail and at least one running carriage which can be connected to the furniture door and which has at least one rolling body (6a, 6b), by way of which the at least one running carriage is mounted moveably on the at least one first guide rail, wherein the at least one first guide rail has at least one running surface (7a, 7b) for the at least one rolling body (6a, 6B) of the at least one running carriage, wherein the at least one first guide rail is composed in the longitudinal direction of at least a first rail portion and a second rail portion, wherein the two rail portions (4a, 4b) can be releasably connected by way of at least one connecting portion at which there is provided a portion (A1, A2) of the at least one running surface (7a, 7b) for the at least one rolling body (6a, 6b) of the at least one running carriage, wherein the rail portions (4a, 4b) of the at least one first guide rail can be positioned relative to each other with the at least one connecting portion by way of at least one respective positioning device (K1, K2, G1, G2), wherein the at least one positioning device (K1, K2, G1, G2) has at least one wedge (K1, K2) and at least one corresponding counterpart shape (G1, G2), and the rail portions (4a, 4b) of the at least one first guide rail each have at least one adaptor portion, by way of which the rail portions (4a, 4b) can be releasably connected to the at least one connecting portion, preferably by way of a screw and/or clamping connection, wherein the at least one adaptor portions have at least one wedge and wherein the at least one connecting portion is of a mirror-image symmetrical relationship relative to a central plane, characterized in that the at least one adaptor portions have further wedges which, when the adaptor portions are connected to the at least one connecting portion, cooperate with further counterpart shapes of the at least one connecting portion and in that the at least one connecting portion has a central bar so that the at least one adaptor portions do not bear against each other upon being connected by way of the at least one connecting portion. wherein the rail portions (4a, 4b) of the at least one first guide rail can be positioned relative to each other with the at least one connecting portion by way of at least one respective positioning device (K1, K2, G1, G2), wherein the at least one positioning device (K1, K2, G1, G2) has at least one wedge (K1, K2) and at least one corresponding counterpart shape (G1, G2), and the rail portions (4a, 4b) of the at least one first guide rail each have at least one adaptor portion, by way of which the rail portions (4a, 4b) can be releasably connected to the at least one connecting portion, preferably by way of a screw and/or clamping connection, wherein the at least one adaptor portions have at least one wedge and wherein the at least one connecting portion is of a mirror-image symmetrical relationship relative to a central plane, characterized in that the at least one adaptor portions have further wedges which, when the adaptor portions are connected to the at least one connecting portion, cooperate with further counterpart shapes of the at least one connecting portion and in that the at least one connecting portion has a central bar so that the at least one adaptor portions do not bear against each other upon being connected by way of the at least one connecting portion.