With the number of interconnected devices, many of which being wireless, exceeding the human population, there is a need to power resource-constrained devices through means other than disposable batteries. Harvesting ambient energy from the vicinity of the device is one solution.SKF, a producer of rolling element bearings, produces approximately one billion bearings per year. If parts of the produced bearings could be self-sucient devices powered through ambient energy, the smart integration of electronics in mechanical systems could be achieved. A scenario in which rolling element bearings are embedded with electronics is presented, through which the development of new services, data collection, data transfer and data interpretation can be realized. This scenario is the key motivation for thisthesis.This thesis presents some of the most common sources of energy used for harvesting energy in rotating environments and discusses how dierent transduction methods can convert ambient energy into electrical energy. Finding a general, robust and cost-eectivetechnology that can be applied to or in the vicinity of a rotating system is one of the main focuses of this thesis. The investigated technologies should be applicable to a dirty and encapsulated industrial environment; therefore, certain energy sources, e.g., sun light and radio frequencies, are not investigated. Advancements in vibrational energy harvesting are also presented in the form of a parameterized SPICE model of a piezoelectric vibrationharvester that can be simulated in conjunction with non-ideal and non-linear circuit models. The SPICE model is used to verify the performance of a novel energy harvesting circuit that actively extracts energy from a piezoelectric transducer. The harvesting circuit enables the enforcement of greater electrical damping on the mechanical system, thereby enabling more electrical energy to be extracted. For weak electromechanically coupled piezoelectric harvesters, the circuit can increase the power output by more than 300% compared to a full-wave rectifying bridge. The simulation results with the modeledharvester under the dened operating conditions in conjunction with the active harvesting circuit indicate that an average of more than 1 mW of power can be extracted, which is assumed to be sucient for powering a resource-constrained embedded device.