Sliding door assembly comprising a running rail which defines a longitudinal axis (X) and has a side web and an upper web , a door leaf which is displaceable parallel to a plane (E) formed by the longitudinal axis (X) and a vertical axis (Z) perpendicular to the longitudinal axis (X), wherein the door leaf is suspended from two carriages guided in the running rail , a damper connected to the door leaf , which is arranged between the two carriages and has a driver , and an activator which has a coupling element which co-operates with the driver and which is disengaged from the driver in a disengaged position and engaged with the driver in an engaged position, wherein the activator has a retaining portion which is received in a guide recess formed on an underside of the upper web , wherein the guide recess is delimited on a side facing the carriage by an inner guide portion and an outer guide portion , wherein a longitudinal slot with a width (d 31 ) is formed between the two guide portions , and wherein the retaining portion has projections which are arranged in the guide recess and engage behind the guide portions , characterised in that the activator is designed to be rotatable about the vertical axis (Z) by a limited angular range into a blocking position, in which a transverse extension of the retaining portion orientated perpendicular to the longitudinal axis (X) is greater than the width (d 31 ) of the longitudinal slot and less than or equal to a clear width (d 39 ) of the guide recess , and into a release position, in which a transverse extension of the retaining portion aligned perpendicular to the longitudinal axis (X) is less than or equal to the width (d 31 ) of the longitudinal slot , wherein the projections engage behind the guide portions in the blocking position. a running rail which defines a longitudinal axis (X) and has a side web and an upper web , a door leaf which is displaceable parallel to a plane (E) formed by the longitudinal axis (X) and a vertical axis (Z) perpendicular to the longitudinal axis (X), wherein the door leaf is suspended from two carriages guided in the running rail , a damper connected to the door leaf , which is arranged between the two carriages and has a driver , and an activator which has a coupling element which co-operates with the driver and which is disengaged from the driver in a disengaged position and engaged with the driver in an engaged position, wherein the activator has a retaining portion which is received in a guide recess formed on an underside of the upper web , wherein the guide recess is delimited on a side facing the carriage by an inner guide portion and an outer guide portion , wherein a longitudinal slot with a width (d 31 ) is formed between the two guide portions , and wherein the retaining portion has projections which are arranged in the guide recess and engage behind the guide portions , characterised in that the activator is designed to be rotatable about the vertical axis (Z) by a limited angular range into a blocking position, in which a transverse extension of the retaining portion orientated perpendicular to the longitudinal axis (X) is greater than the width (d 31 ) of the longitudinal slot and less than or equal to a clear width (d 39 ) of the guide recess , and into a release position, in which a transverse extension of the retaining portion aligned perpendicular to the longitudinal axis (X) is less than or equal to the width (d 31 ) of the longitudinal slot , wherein the projections engage behind the guide portions in the blocking position. <EOS>