This book provides both theoretical foundations and practical insights into linear and nonlinear crystal optics. It bridges the fundamental principles of light-crystal interactions with advanced applications in optics. Linear and Nonlinear Crystal Optics offers a thorough exploration of electric susceptibility—the cornerstone of optical properties through electric constitutive relations and Maxwell’s equations. Key features include comprehensive tensor representations, detailed angular distributions of optical parameters, complete mathematical demonstrations, and original research insights developed over decades. The book covers essential topics including phenomenological introduction to light-matter coupling, mathematical background in orientation and thermodynamic symmetries, electric susceptibility and field tensors, polarization calculations, linear optical effects linked to the real and imaginary parts of the refractive index, and both second-order and third-order interactions. Each chapter concludes with a summary and references, providing readers with clear learning pathways and resources for further exploration. This book is ideal for advanced undergraduate students, graduate students, and researchers in physics, optical engineering, materials science, and crystallography. It serves as an essential reference for professionals working in fields requiring deep understanding of crystal optics, including photonics, laser technology, telecommunications, and materials characterization.