Magnetic reconnection at the dayside magnetopause is one of the most important mechanisms that efficiently transfers solar wind particles, momentum, and energy into the Earth's magnetosphere. Cold dense plasma, originating either directly from the ionosphere or from the plasmasphere, has often been observed at the adjacent magnetopause. These cold plasmas may affect reconnection since they modify the plasma properties on the magnetospheric side significantly. Case and statistical studies of the characteristics of the cold ions observed at the dayside magnetopause are presented by using Cluster spacecraft datasets. The behavior of the cold dense plasma of ionospheric origin during magnetic reconnection at the dayside magnetopause, occurrence rates of plasmaspheric plumes and ionospheric outflows, and their dependence on the solar wind/Interplanetary Magnetic Field (IMF) conditions have been investigated. Finally, a controlling factor that leads to the asymmetric reconnection geometry at the magnetopause has been examined.