After decades of developments in the miniaturization of portable and wireless devices, new power sources beyond rechargeable batteries have become important topics for current and future stand-alone devices and systems. Specifically, ideal power sources should be scalable for the power demands of various portable devices without the necessity of a recharging process or replacement. Recent works in the field of nanomaterials have shown good progress toward self-powered energy sources by scavenging energy from ambient environments (solar, thermal, mechanical vibration, etc.). In particular, the use of piezoelectric generators by nanomaterials as a robust and simple solution for mechanical energy harvesting has attracted a lot of attention. One of the earliest nanogenerators for possible energy scavenging applications from mechanical strain utilized piezoelectric zinc oxide (ZnO) nanowires.¹  By coupling their semiconducting and piezoelectric properties, mechanical strains can be converted into electricity. In recent years, numerous research groups have demonstrated results in the field of mechanical energy scavenging using nanomaterials with different architectures, including: film-based, nanowire-based and nanofiber-based nanogenerators. Film-based nanogenerators are often made by the spin-on or thin-film deposition methods.^2,3  Mechanical strains due to bending, vibration or compression of the thin-film structure can be the sources of energy generation. Nanowire-based nanogenerators⁴  are typically made of semiconducting materials such as ZnO,^1,5,6  ZnS,⁷  GaN^8,9  or CdS.^10,11  These piezoelectric nanowires have been demonstrated to build up an electrical potential when mechanically strained by AFM tips,¹  zig-zag electrodes¹²  or compliant substrates¹³  to convert mechanical strains into electricity. The third group of nanogenerators is based on nanofibers often constructed by the electrospinning process to be discussed in detail in this chapter.