The paper provides a comprehensive tutorial on the theory of spread-spectrum communications, covering its applications, properties of common spreading sequences, and techniques for acquisition and tracking. Spread-spectrum systems, developed since the mid-1950s, are used in various systems, including military antijamming, code division multiple access (CDMA), and multipath mitigation. The key advantage of spread-spectrum is its ability to reduce interference, allowing multiple users to share the same spectral band. The paper discusses the fundamental principles of spread-spectrum, including the concept of dimensionality and processing gain, which explains how the technique protects against finite-power interference. It also covers pseudorandom sequence generators, their properties, and their use in spread-spectrum systems. The paper further explores anti-jam considerations, focusing on the performance of direct-sequence (DS) and frequency-hopping (FH) systems in the presence of jamming signals. Additionally, it delves into CDMA, explaining how it allows simultaneous transmission from multiple users in the same frequency band and addressing the "near-far problem" and the use of error-correction coding. The paper concludes by comparing the capacity and advantages of CDMA with other multiple-access techniques like FDMA and TDMA.The paper provides a comprehensive tutorial on the theory of spread-spectrum communications, covering its applications, properties of common spreading sequences, and techniques for acquisition and tracking. Spread-spectrum systems, developed since the mid-1950s, are used in various systems, including military antijamming, code division multiple access (CDMA), and multipath mitigation. The key advantage of spread-spectrum is its ability to reduce interference, allowing multiple users to share the same spectral band. The paper discusses the fundamental principles of spread-spectrum, including the concept of dimensionality and processing gain, which explains how the technique protects against finite-power interference. It also covers pseudorandom sequence generators, their properties, and their use in spread-spectrum systems. The paper further explores anti-jam considerations, focusing on the performance of direct-sequence (DS) and frequency-hopping (FH) systems in the presence of jamming signals. Additionally, it delves into CDMA, explaining how it allows simultaneous transmission from multiple users in the same frequency band and addressing the "near-far problem" and the use of error-correction coding. The paper concludes by comparing the capacity and advantages of CDMA with other multiple-access techniques like FDMA and TDMA.