A dual-mode ion detector for a mass and/or ion mobility spectrometer, the detector comprising: a first conversion electrode that is maintained, in use, at a negative potential and arranged for converting incident positive ions into secondary electrons; a second conversion electrode that is maintained, in use, at a positive potential and arranged for converting incident negative ions into secondary positive ions and/or secondary electrons; an electron detecting surface; and an entrance electrode for drawing ions into the ion detector, the entrance electrode comprising a ring electrode, wherein the ion detector is switchable between a first mode for detecting positive ions and a second mode for detecting negative ions, wherein in the first mode a negative voltage is applied to the entrance electrode to draw incoming positive ions into the ion detector so that an incoming positive ion is drawn into the ion detector by the entrance electrode and is then accelerated towards and caused to initially strike the first conversion electrode to create secondary electrons, whereas in the second mode a positive voltage is applied to the entrance electrode to draw incoming negative ions into the ion detector so that an incoming negative ion is drawn into the ion detector and is then accelerated towards and caused to initially strike the second conversion electrode to create secondary positive ions and/or secondary electrons, wherein the first conversion electrode is arranged and shaped so that secondary electrons created by positive ions striking the first conversion electrode are then caused to strike the electron detecting surface, and wherein: (i) the second conversion electrode is arranged and shaped so that secondary positive ions created by negative ions striking the second conversion electrode are then caused to strike the first conversion electrode to create secondary electrons which are in turn caused to strike the electron detecting surface, and/or (ii) the second conversion electrode is arranged and shaped so that secondary electrons created by negative ions striking the second conversion electrode are then caused to strike the electron detecting surface. a first conversion electrode that is maintained, in use, at a negative potential and arranged for converting incident positive ions into secondary electrons; a second conversion electrode that is maintained, in use, at a positive potential and arranged for converting incident negative ions into secondary positive ions and/or secondary electrons; an electron detecting surface; and an entrance electrode for drawing ions into the ion detector, the entrance electrode comprising a ring electrode, wherein the ion detector is switchable between a first mode for detecting positive ions and a second mode for detecting negative ions, wherein in the first mode a negative voltage is applied to the entrance electrode to draw incoming positive ions into the ion detector so that an incoming positive ion is drawn into the ion detector by the entrance electrode and is then accelerated towards and caused to initially strike the first conversion electrode to create secondary electrons, whereas in the second mode a positive voltage is applied to the entrance electrode to draw incoming negative ions into the ion detector so that an incoming negative ion is drawn into the ion detector and is then accelerated towards and caused to initially strike the second conversion electrode to create secondary positive ions and/or secondary electrons, wherein the first conversion electrode is arranged and shaped so that secondary electrons created by positive ions striking the first conversion electrode are then caused to strike the electron detecting surface, and wherein: (i) the second conversion electrode is arranged and shaped so that secondary positive ions created by negative ions striking the second conversion electrode are then caused to strike the first conversion electrode to create secondary electrons which are in turn caused to strike the electron detecting surface, and/or (ii) the second conversion electrode is arranged and shaped so that secondary electrons created by negative ions striking the second conversion electrode are then caused to strike the electron detecting surface. (i) the second conversion electrode is arranged and shaped so that secondary positive ions created by negative ions striking the second conversion electrode are then caused to strike the first conversion electrode to create secondary electrons which are in turn caused to strike the electron detecting surface, and/or (ii) the second conversion electrode is arranged and shaped so that secondary electrons created by negative ions striking the second conversion electrode are then caused to strike the electron detecting surface.