Securing device for a lift-and-slide door that can be mounted in the gap of the central abutment region of mutually overlapping vertical frame profiles (10, 20) of the sliding leaf and of the fixed leaf of a lift-and-slide door, comprising a. a first securing element, in particular for fastening to one of the two leaves, and b. a second securing element, in particular for fastening to the other leaf, c. wherein the securing elements (50, 60) can be brought into engagement with one another and out of engagement by movement, in particular of at least one of the securing elements, in an engagement direction which corresponds to an intended horizontal sliding direction of a sliding leaf, d. wherein, with existing engagement, in particular at least after mounting of the securing elements (50, 60) on frame profiles (10, 20) of a lift-and-slide door, the separation of the securing elements (50, 60) in directions perpendicular to the engagement direction is prevented, and e. the first securing element, in particular the securing element intended for fastening to a fixed leaf, has at least one passage region which is open in the engagement direction and which is adjoined at least in certain regions by a wall region of the first securing element, and f. the second securing element has at least one securing tab, in particular a number of securing tabs corresponding to the number of the passage regions, wherein the at least one securing tab extends in the engagement direction and can be inserted into and withdrawn from the first securing element through a passage region, characterized in that g. two projections (53a, 53b) which are opposite one another in a direction perpendicular to the engagement direction and extend away from one another perpendicular to the engagement direction are arranged on the at least one securing tab of the second securing element, in particular at its free end, and can each engage behind a wall of the first securing element that adjoins the passage region, in particular with existing engagement after a relative movement of the securing elements (50, 60) with respect to one another in a direction perpendicular to the engagement direction, and h. the second securing element has at least one fastening tab, in particular with at least one opening, wherein the at least one fastening tab and the at least one securing tab lie in parallel spaced-apart planes, wherein the at least one fastening tab and the at least one securing tab are connected to a spacer wall across the spacing. a. a first securing element, in particular for fastening to one of the two leaves, and b. a second securing element, in particular for fastening to the other leaf, c. wherein the securing elements (50, 60) can be brought into engagement with one another and out of engagement by movement, in particular of at least one of the securing elements, in an engagement direction which corresponds to an intended horizontal sliding direction of a sliding leaf, d. wherein, with existing engagement, in particular at least after mounting of the securing elements (50, 60) on frame profiles (10, 20) of a lift-and-slide door, the separation of the securing elements (50, 60) in directions perpendicular to the engagement direction is prevented, and e. the first securing element, in particular the securing element intended for fastening to a fixed leaf, has at least one passage region which is open in the engagement direction and which is adjoined at least in certain regions by a wall region of the first securing element, and f. the second securing element has at least one securing tab, in particular a number of securing tabs corresponding to the number of the passage regions, wherein the at least one securing tab extends in the engagement direction and can be inserted into and withdrawn from the first securing element through a passage region, characterized in that g. two projections (53a, 53b) which are opposite one another in a direction perpendicular to the engagement direction and extend away from one another perpendicular to the engagement direction are arranged on the at least one securing tab of the second securing element, in particular at its free end, and can each engage behind a wall of the first securing element that adjoins the passage region, in particular with existing engagement after a relative movement of the securing elements (50, 60) with respect to one another in a direction perpendicular to the engagement direction, and h. the second securing element has at least one fastening tab, in particular with at least one opening, wherein the at least one fastening tab and the at least one securing tab lie in parallel spaced-apart planes, wherein the at least one fastening tab and the at least one securing tab are connected to a spacer wall across the spacing.