Near-Field Communications (NFC) is an emerging technology in future wireless systems, leveraging large-scale antenna arrays and high frequencies to enhance wireless network capacity through increased spatial degrees of freedom (DoFs). This survey provides a comprehensive overview of NFC, covering its fundamental principles, channel modeling, performance analysis, signal processing, and integration with emerging technologies. The paper highlights the unique properties of NFC compared to far-field communications (FFC), such as different radiation patterns, field regions, and metrics. It also discusses the challenges and opportunities in NFC applications for next-generation 6G networks. The paper begins by introducing the historical development of NFC, tracing its roots from early wave theories to modern applications. It then explores recent advancements in antenna array technology, including holographic MIMO, reconfigurable intelligent surfaces (RISs), dynamic metasurface antennas (DMAs), and fluid antennas. These technologies enable large aperture sizes and enhanced near-field beamforming capabilities, crucial for NFC. The paper reviews near-field channel models, distinguishing between continuous-aperture (CAP) and spatially-discrete (SPD) antenna arrays. It discusses the physical properties of the near-field region, including different radiation patterns, field regions, and approximations. The paper also introduces EM information theory (EIT) as a fundamental analytical tool for characterizing near-field channels, focusing on DoFs and effective DoFs (EDoFs). Performance evaluation techniques for NFC are presented, considering the reviewed near-field channel models. The paper summarizes current research contributions, outlining their advantages and limitations. Signal processing techniques for NFC, including channel estimation, beamforming design, and low-complexity beam training, are discussed in detail. The paper identifies significant research opportunities in integrating NFC with other emerging technologies, such as integrated sensing and communications (ISAC), RIS, nonorthogonal multiple access (NOMA), wireless power transfer (WPT), simultaneous wireless information and power transfer (SWIPT), and physical layer security (PLS). It discusses potential solutions and avenues for future exploration. The paper is structured into sections covering the fundamentals of NFC, near-field channel models, performance analysis, signal processing techniques, integration with emerging technologies, and conclusions. It provides a comprehensive review of NFC principles, channel models, performance analysis, signal processing, and integration with emerging technologies, highlighting the unique properties of NFC and its potential applications in next-generation wireless networks.Near-Field Communications (NFC) is an emerging technology in future wireless systems, leveraging large-scale antenna arrays and high frequencies to enhance wireless network capacity through increased spatial degrees of freedom (DoFs). This survey provides a comprehensive overview of NFC, covering its fundamental principles, channel modeling, performance analysis, signal processing, and integration with emerging technologies. The paper highlights the unique properties of NFC compared to far-field communications (FFC), such as different radiation patterns, field regions, and metrics. It also discusses the challenges and opportunities in NFC applications for next-generation 6G networks. The paper begins by introducing the historical development of NFC, tracing its roots from early wave theories to modern applications. It then explores recent advancements in antenna array technology, including holographic MIMO, reconfigurable intelligent surfaces (RISs), dynamic metasurface antennas (DMAs), and fluid antennas. These technologies enable large aperture sizes and enhanced near-field beamforming capabilities, crucial for NFC. The paper reviews near-field channel models, distinguishing between continuous-aperture (CAP) and spatially-discrete (SPD) antenna arrays. It discusses the physical properties of the near-field region, including different radiation patterns, field regions, and approximations. The paper also introduces EM information theory (EIT) as a fundamental analytical tool for characterizing near-field channels, focusing on DoFs and effective DoFs (EDoFs). Performance evaluation techniques for NFC are presented, considering the reviewed near-field channel models. The paper summarizes current research contributions, outlining their advantages and limitations. Signal processing techniques for NFC, including channel estimation, beamforming design, and low-complexity beam training, are discussed in detail. The paper identifies significant research opportunities in integrating NFC with other emerging technologies, such as integrated sensing and communications (ISAC), RIS, nonorthogonal multiple access (NOMA), wireless power transfer (WPT), simultaneous wireless information and power transfer (SWIPT), and physical layer security (PLS). It discusses potential solutions and avenues for future exploration. The paper is structured into sections covering the fundamentals of NFC, near-field channel models, performance analysis, signal processing techniques, integration with emerging technologies, and conclusions. It provides a comprehensive review of NFC principles, channel models, performance analysis, signal processing, and integration with emerging technologies, highlighting the unique properties of NFC and its potential applications in next-generation wireless networks.