Effective geophysical exploration of mineral resources is dependent on selecting proper instrumentation, best suited to the prospective application. In order to make informed decisions about instrument selection, it is important to have an understanding of the differences between general instrument classifications and their respective best-suited applications as well as the underlying physical principles that differentiate device types. We provide an overview of fundamental electromagnetic systems: sensor, receiver, and transmitter; with a focus on general application, and system design considerations with an emphasis on time-domain electromagnetics. Primary focus is on current commercially available technology, with a brief look at emerging technologies.