Open problems in nonlinear dynamics and chaos include understanding the long-term behavior of chaotic systems, the predictability of chaotic phenomena, and the transition between different dynamical regimes. Researchers are also focused on the mathematical characterization of strange attractors and the implications of chaos in various fields such as physics and biology. The challenges involve developing robust methods for analyzing complex systems and improving computational techniques for simulating chaotic behavior. Additionally, there is ongoing exploration of the connections between chaos theory and other scientific disciplines. Addressing these issues could significantly advance the understanding of nonlinear dynamics and its applications.