Harmonic suppression in bulk acoustic wave duplexer. In some embodiments, a filter circuit can include an input node and an output node, and a first assembly having one or more bulk acoustic wave (BAW) resonators implemented electrically between the input node and the output node, and configured to filter a signal. The filter circuit can further include a second assembly having one or more surface acoustic wave (SAW) resonators implemented electrically relative to the first assembly, and configured to suppress one or more harmonics resulting from the filtering of the signal by the first assembly.