Improved performances, compact size, and lower cost are the key driving factors for advancement of modern communication systems. To meet these stringent requirements, defected ground structures (DGS) can be an effective tool. In this article, a comprehensive review of various DGS configurations emphasizing the background and evolution, classification, equivalent circuit modeling techniques, and their applications in different areas of microwave engineering has been presented. A review of different DGS‐engineered band stop filters (BSFs), low‐pass filters (LPFs), and high‐performance band‐pass filters (BPFs) is included. An overview of the applications of DGS in performance improvements of microwave antennas in terms of impedance matching, size reduction, spurious response suppression, mutual coupling reduction, cross‐polarized radiation suppression, and application of DGS in accomplishing a beam‐steering operation for a phased array antenna has also been included. Radio frequency identification (RFID) and microwave sensors, which are finding increased application, are introduced, and applications of DGS in conventional and chipless RFID tag design as well as in low‐cost passive microwave sensor implementation are also discussed. Additionally, applications of DGS in high‐impedance microstrip line realization and in output power and operational efficiency enhancement of microwave active circuits like oscillators and power amplifiers are covered. Finally, some limitations and challenges of DGS implementation in microwave circuits and antennas are discussed. Overall, adaptation of DGS in conventional passive and active microwave applications and in new emerging fields, like RFID and sensors, are covered in this article.