This review article focuses on the defects and defect engineering of two-dimensional (2D) transition metal dichalcogenides (TMDCs). TMDCs, with their layered structure, exhibit unique properties such as tunable electrical, optical, and magnetic characteristics, making them promising materials for various applications. However, these materials are prone to intrinsic and extrinsic defects, which can significantly impact their performance. The article discusses the fundamental structure of TMDCs, including their different types of defects (zero-dimensional, one-dimensional, and two-dimensional), and reviews existing defect characterization tools and defect engineering methods. It also explores how defects affect the electronic, optical, and magnetic properties of TMDC materials. The review highlights the importance of controlling defects in TMDC materials to optimize their performance in next-generation nanoelectronics and optoelectronics devices.This review article focuses on the defects and defect engineering of two-dimensional (2D) transition metal dichalcogenides (TMDCs). TMDCs, with their layered structure, exhibit unique properties such as tunable electrical, optical, and magnetic characteristics, making them promising materials for various applications. However, these materials are prone to intrinsic and extrinsic defects, which can significantly impact their performance. The article discusses the fundamental structure of TMDCs, including their different types of defects (zero-dimensional, one-dimensional, and two-dimensional), and reviews existing defect characterization tools and defect engineering methods. It also explores how defects affect the electronic, optical, and magnetic properties of TMDC materials. The review highlights the importance of controlling defects in TMDC materials to optimize their performance in next-generation nanoelectronics and optoelectronics devices.