Superconducting nanowire single-photon detectors (SNSPDs) have emerged as a highly promising technology for infrared photon counting. These detectors offer high efficiency, low dark counts, and excellent timing resolution. This review discusses the basic operating principle of SNSPDs, their evolution in design, performance improvements, and practical considerations such as cooling, optical coupling, and readout circuits. It also surveys promising applications, ranging from quantum cryptography to remote sensing. SNSPDs operate at the boiling point of liquid helium (4.2 K), a temperature now achievable with improved cooling technology. They are superior to other single-photon detectors in terms of signal-to-noise ratio and are suitable for time-correlated single-photon counting (TCSPC) in the infrared regime. SNSPDs have been the subject of intense research over the past decade, with many groups contributing to their development. The review aims to summarize the basic device operating principle, evolution of SNSPD design, refrigeration and materials considerations, and promising applications. SNSPDs are highly sensitive to single photons and have been used in quantum key distribution (QKD), optical quantum computing, characterization of quantum emitters, space-to-ground communications, integrated circuit testing, fibre temperature sensing, and time-of-flight depth ranging. Their performance is influenced by factors such as coupling efficiency, absorption efficiency, and registering efficiency. The review also discusses noise mechanisms, including dark counts and timing jitter, and the importance of minimizing these to improve detector performance. The review concludes that SNSPDs are a promising technology for a wide range of applications, and their continued development is essential for advancing quantum information science and other fields.Superconducting nanowire single-photon detectors (SNSPDs) have emerged as a highly promising technology for infrared photon counting. These detectors offer high efficiency, low dark counts, and excellent timing resolution. This review discusses the basic operating principle of SNSPDs, their evolution in design, performance improvements, and practical considerations such as cooling, optical coupling, and readout circuits. It also surveys promising applications, ranging from quantum cryptography to remote sensing. SNSPDs operate at the boiling point of liquid helium (4.2 K), a temperature now achievable with improved cooling technology. They are superior to other single-photon detectors in terms of signal-to-noise ratio and are suitable for time-correlated single-photon counting (TCSPC) in the infrared regime. SNSPDs have been the subject of intense research over the past decade, with many groups contributing to their development. The review aims to summarize the basic device operating principle, evolution of SNSPD design, refrigeration and materials considerations, and promising applications. SNSPDs are highly sensitive to single photons and have been used in quantum key distribution (QKD), optical quantum computing, characterization of quantum emitters, space-to-ground communications, integrated circuit testing, fibre temperature sensing, and time-of-flight depth ranging. Their performance is influenced by factors such as coupling efficiency, absorption efficiency, and registering efficiency. The review also discusses noise mechanisms, including dark counts and timing jitter, and the importance of minimizing these to improve detector performance. The review concludes that SNSPDs are a promising technology for a wide range of applications, and their continued development is essential for advancing quantum information science and other fields.