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Recent interest in the technological potential of nitride-based semiconductors has led to the development and commercialization of a wide range of electronic devices. The nanoscale investigation of the electric properties of III-nitride thin films, bulk crystals, and heterostructures is of considerable interest for determining how interfaces, defects, and inversion domain boundaries affect device performance. The pyroelectric nature of wurtzitic III-nitrides is characterized by a spontaneous polarization that exists without the presence of an external field and by a polarization-bound surface charge. Scanning probe-based measurements of surface contact potentials and surface band bending in these materials, which are of crucial importance to device design, are summarized in this review chapter. In addition, the role of charged defects on device performance is explored by scanning probe techniques. Lastly, the measurement of polarity and of the screening mechanism of III-nitrides, which are fundamental issues for the fabrication of devices based on polarity effects, are discussed. This chapter provides a critical analysis of the contributions made by scanning probe-based techniques toward a deeper understanding of the III-nitride material system.