Control under uncertainty is one of the main focuses of modern control theory research. The idea of sliding mode and higher-order sliding-mode control (SMC/HOSMC) is to drive the system trajectory to properly chosen constraints (sliding manifold) in finite time and preserving the constraints for all subsequent time by means of high-frequency switching control. The main features of SMC/HOSMC are its insensitivity to bounded disturbances matched to the control, high stabilization accuracy, and finite-time convergence. Therefore, SMC/HOSMC remains, probably, one of the most popular choices for handling systems with bounded uncertainties/disturbances. Adaptive HOSMC has been of great interest in the sliding-mode control community during the last 15 years due to its ability to handle perturbations with unknown bounds while mitigating chattering, if the adaptive control gains are not overestimated. This chapter presents an overview of the adaptive SMC/HOSMC paradigms and algorithms. A number of application specific results are also discussed. The literature in the area is presented in the context of continuing developments in the broad areas of the theory and application of adaptive SMC/HOSMC.