AbstractWe present Cluster spacecraft observations of large‐amplitude (δ|B|/|B|∼1) fast‐mode magnetosonic waves in the heliospheric current sheet (HCS). The crossings of the HCS and the associated heliospheric plasma sheet (HPS) are encountered by Cluster in the near‐Earth solar wind and by ACE upstream of Earth. Multiple current layers are detected in correspondence with small‐scale discontinuities in the regime of open magnetic field lines within the HCS. Fast magnetosonic waves are observed at one current layer, accompanying the phase‐steeped edge of a large‐amplitude transverse Alfvén wave. The observed fast‐mode waves are in the frequency range 0.01 Hz–0.2 Hz, characterized by a strong correlation between variations of plasma density and magnetic field strength. Analysis of ratio δE/δBindicate that the fast‐mode wave packet consists of an antisunward propagating component and a larger sunward propagating component in the rest frame of the solar wind. The fast‐mode waves are not observed by ACE in the upstream solar wind. The generation of the fast‐mode waves may relate to the development of the phase‐steeped Alfvén wave and has profound effects on the evolution of the solar wind plasma.