In recent years, the THz part of the electromagnetic spectrum has attracted special attention due to the broad range of possible applications deriving from it and its presence in multiple natural phenomena. T-rays are able to pass almost unobstructed through a wide range of non-polar materials such as fabrics, paper, wood, ceramics, plastics and plasma. Radioastronomy, spectroscopy, molecular sensing, plasma diagnostics, security and biomedical imaging are only a few possible uses of the THz spectrum. Such wide range of possible applications demands a similarly wide range of detection techniques and devices. The methods presented in this overview have been organized in four groups, based on the physical principia they rely on: thermal, direct detection, superhet and sampling detection. For each of the techniques, the operational limits and the most frequent applications are also presented.