Plug-in connection, comprising a male plug part and a female plug part, wherein the male plug part can be inserted or is inserted into the female plug part along a connection axis, wherein the two plug parts (9, 11) have a rectangular cross section along a connection plane, wherein the female plug part can be connected to the inserted male plug part by means of a U-shaped holding clip, which is guided on the female plug part, and assumes a latching position and an operating position, characterized in that the holding clip comprises a connection web with a first and a second connection end (3a, 3b), wherein a locking web and a guide web are integrally formed at the two connection ends (3a, 3b) perpendicular to the connection web along a holding clip extent axis in a manner separated by a slot in each case, wherein the female plug part has a U-shaped outer groove, and the holding clip is fitted onto the outer groove, and the outer groove comprises in each case one aperture on its two opposite limbs, and the free ends of the locking webs have latching projections which face one another towards the inside and the two guide webs have stop cams on their bottom sides which are averted from the locking webs, wherein each guide web comprises, on its inner faces which face one another, holding ribs which project from the said inner faces and extend along a holding clip extent axis, and a holding rib and a shoulder of the holding clip pass through the respective aperture, wherein the holding ribs and the shoulders, when the male plug part is in the inserted state, interact with guide cams (37a, 37b), which are arranged on the said male plug part, and a holding lug in such a way that the holding clip can assume a pre-mounting position, the latching position, the operating position and a removal position, wherein the pre-mounting position is that position which the holding clip assumes before the guide cams (37a, 37b) make contact with the shoulders along the connection axis, wherein the latching projections engage into a window in a transfer position of the holding clip from the pre-mounting position to the latching position, wherein, in the latching position, each of the two latching projections is pressed through the respective guide cam (37a, 37b) out of the respective window when the plug parts (9, 11) are in the plugged state, as a result of which the locking web assumes a spread position, and the latching position occurs when the holding rib latches in in an interlocking manner behind the holding lug which is arranged on the male plug part in the penetration direction of the male plug part, and the operating position is the position of the holding clip when the fixing positioning of the two plug parts (9, 11) is completed, wherein a pseudo plug-in connection is precluded, wherein the outer groove has in each case one outer groove end which is correlated with the free ends of the locking webs and guide webs, wherein the outer groove end has a guide shoulder which rises conically along the holding clip extent axis for the locking web and for the guide web in each case, the locking web and the guide web being mounted in a sliding manner on the said guide shoulder in the removal position, and wherein, in the removal position, the connection web of the holding clip is pressed along the holding clip extent axis in the direction of the free ends of the locking webs and of the guide webs and the connection web stops on the female plug part, and wherein the holding clip, as a plug-in indicator, indicates whether the female and the male plug part (9, 11) are fully plugged one into the other.