CRISPR-Cas nucleases have changed the world of genetic editing because they provides specific, programmable and scalable editing possibilities. These RNA-guided nucleases were first described in the adaptive immune systems of prokaryotes, but have since enjoyed a second incarnation in eukaryotes, where they edit pathogenic mutations, control transcription, and even alter epigenetic structure. The field of structural biology has shown distinctly varied architecture among Cas nucleases, such as Cas9, Cas12, Cas13, and newly studied variants, and has shown the conserved catalytic cores, RNA guide recognition elements, and ever-changing structural dynamics of the target and the controls that modulate its cleavage effectiveness. Biochemical analyses have shed light on the mechanisms of interrogating DNA, forming R-loops, allosteric activation, and collateral activity, guiding the engineering approaches to improve fidelity and minimize off-target effects. Although substantial progress has been made, there remains the challenge of achieving single-nucleotide precision and reducing genotoxicity, as well as improving delivery efficiency to a wide variety of cell and tissue types. Advanced innovations in high-fidelity variants, base, prime editing, and Anti-CRISPR controllers have broadened their application and improved their safety profiles. While clinical trials for monogenic disorders like sickle cell disease and Leber congenital amaurosis have noted early successes, their long-term efficacy, immunogenicity, and ethical issues remain significant obstacles. This review integrates biochemistry and structural biology of CRISPR-Cas nucleases and focuses on mechanisms of their function and engineering that are central to the CRISPR-Cas Rational Design. The application of structural biology in conjunction with functional genomics and translational medicine aids in a refined and well-integrated understanding of the mechanisms guiding the evolution of CRISPR therapeutics. This review analyses the role of atomic resolution structures in guiding protein engineering, the role of kinetic and thermodynamic parameters in determining editing outcomes, and the role of evolutionary divergence in informing the selection of nucleases for specific purposes. Emerging trends, which include the use of compact CAS enzymes for viral delivery, RNA-targeting systems for the transient modulation of gene expression, and synthetic regulatory modules for the systems engineering of CRISPR, promise to augment the clinical reach of CRISPR therapeutics. These variances in application outline the junction of editing outcomes and the evolvable Technomic of CRISPR.