Channel state information is reported in periodic and aperiodic reports for multiple component carriers or serving cells. Channel state information may be reported for a subset of aggregated downlink carriers or serving cells. For an aperiodic report, the carrier(s)/serving cell(s) for which channel state information is reported may be determined based on the request for the aperiodic report. A report collision may occur in a subframe between a periodic CSI report for a first serving cell and a report for a second serving cell. A priority rule may be used to resolve the report collision.