Advances in terahertz (THz) communications have been significantly accelerated by photonics technologies. Over the past 15 years, THz wireless communications have evolved from initial demonstrations using impulse and continuous waves to more advanced systems. THz technologies are gaining interest due to the increasing demand for higher data rates in wireless communications. This article reviews the role of photonics in THz communication systems and compares them with other technologies like THz transceivers using electronic devices and free-space optical communications. Data traffic is increasing exponentially, with IP traffic expected to reach over 130 Exabytes per month by 2018. This growth is driven by wireless channels, requiring higher transmission rates. The potential data rate for wireless communications is expected to reach 100 Gbit/s within 10 years. Historically, carrier frequencies have increased to meet bandwidth requirements, but the available bandwidth is limited, making THz frequencies more promising for high data rates. THz waves in the range of 0.1 THz to 10 THz offer large bandwidths, but atmospheric attenuation limits their use. The optimal carrier frequencies depend on the transmission distance. For example, 100 GHz to 150 GHz is suitable for long-distance communications, while higher frequencies are used for shorter distances. THz communication systems face challenges such as atmospheric absorption and rain attenuation, which affect transmission distance. Photonics-based THz communication systems use photomixing and optical coherent technologies to achieve high data rates. Photonic devices enable multi-carrier transmission and high-speed modulation. Recent advancements include photonic transmitters with data rates up to 100 Gbit/s. However, challenges remain in power limitations and signal stability. Electronic-based THz systems use waveguide devices and GaAs/InP transistors for high-frequency applications. These systems have achieved data rates up to 50 Gbit/s. However, they face limitations in power and modulation index. Future developments in THz communications include photonic integration, which reduces coupling losses and enables advanced antenna systems. Silicon photonics and III-V technologies are promising for high integration and performance. Amplification techniques and hybrid systems are also being explored to improve THz communication efficiency. THz communication systems require careful consideration of link budget, signal processing, and power consumption. Photonics-based systems offer advantages in handling multi-carrier and multi-format channels. However, challenges such as energy consumption and signal stability need to be addressed for practical deployment. The future of THz communications depends on advancements in photonic and electronic technologies, including integrated circuits, amplifiers, and efficient modulation schemes. Standardization and spectrum regulation are also critical for widespread adoption. Overall, THz communications hold great potential for high-speed, high-capacity wireless networks.Advances in terahertz (THz) communications have been significantly accelerated by photonics technologies. Over the past 15 years, THz wireless communications have evolved from initial demonstrations using impulse and continuous waves to more advanced systems. THz technologies are gaining interest due to the increasing demand for higher data rates in wireless communications. This article reviews the role of photonics in THz communication systems and compares them with other technologies like THz transceivers using electronic devices and free-space optical communications. Data traffic is increasing exponentially, with IP traffic expected to reach over 130 Exabytes per month by 2018. This growth is driven by wireless channels, requiring higher transmission rates. The potential data rate for wireless communications is expected to reach 100 Gbit/s within 10 years. Historically, carrier frequencies have increased to meet bandwidth requirements, but the available bandwidth is limited, making THz frequencies more promising for high data rates. THz waves in the range of 0.1 THz to 10 THz offer large bandwidths, but atmospheric attenuation limits their use. The optimal carrier frequencies depend on the transmission distance. For example, 100 GHz to 150 GHz is suitable for long-distance communications, while higher frequencies are used for shorter distances. THz communication systems face challenges such as atmospheric absorption and rain attenuation, which affect transmission distance. Photonics-based THz communication systems use photomixing and optical coherent technologies to achieve high data rates. Photonic devices enable multi-carrier transmission and high-speed modulation. Recent advancements include photonic transmitters with data rates up to 100 Gbit/s. However, challenges remain in power limitations and signal stability. Electronic-based THz systems use waveguide devices and GaAs/InP transistors for high-frequency applications. These systems have achieved data rates up to 50 Gbit/s. However, they face limitations in power and modulation index. Future developments in THz communications include photonic integration, which reduces coupling losses and enables advanced antenna systems. Silicon photonics and III-V technologies are promising for high integration and performance. Amplification techniques and hybrid systems are also being explored to improve THz communication efficiency. THz communication systems require careful consideration of link budget, signal processing, and power consumption. Photonics-based systems offer advantages in handling multi-carrier and multi-format channels. However, challenges such as energy consumption and signal stability need to be addressed for practical deployment. The future of THz communications depends on advancements in photonic and electronic technologies, including integrated circuits, amplifiers, and efficient modulation schemes. Standardization and spectrum regulation are also critical for widespread adoption. Overall, THz communications hold great potential for high-speed, high-capacity wireless networks.