This paper presents a two-dimensional (2-D) piecewise model for the dynamic behavioral modeling and digital predistortion of highly nonlinear dual-band radio frequency (RF) power amplifiers (PAs). The model performance was validated in two cases: an envelope-tracking dual-band PA and a current-controlled wide-band PA, using carrier-aggregated long-term evolution signals. The proposed model is partitioned according to different functions of composite multi-input amplitudes rather than the single input amplitude. Measurement and simulation results show that this model is much more flexible in modeling highly nonlinear RF transmitters with inconsistent behavior at different multi-input levels. The experimental results for dual-band cases confirm that the 2-D piecewise model can produce better performance than conventional models that have limited performance in characterization of these hard nonlinearities.