This chapter presents a comprehensive overview of the mechanical and rheological properties of polymer gels, emphasizing the distinctive features that set gels apart from conventional solids. Section 6.1 introduces the fundamentals of gel elasticity—such as low elastic moduli, high deformability, and reversible shape changes—arising from the entropic elasticity of their polymer networks. Theoretical developments are traced from the affine and phantom network models to more advanced frameworks that incorporate finite extensibility, network defects, and deformation-mode dependence. Section 6.2 explores diffusio-mechanical coupling, where strain-induced solvent migration leads to time-dependent stress relaxation and swelling/shrinking phenomena. Various deformation scenarios are analyzed, including constant strain, strain rate, oscillatory strain, and compression, along with centrifugal and shear-induced effects. Section 6.3 addresses the sol-gel transition, highlighting its critical behavior through the lens of percolation and fractal theories. The chapter outlines rheological criteria for identifying the gel point—such as power-law scaling of the dynamic modulus—and discuss both universal and system-specific aspects of the critical exponents. Experimental data are examined to link viscoelastic properties with the underlying network structure and dynamics, offering insights into gelation process. Together, the sections illustrate how molecular structure, solvent transport, and mechanical deformation collectively govern the emergent properties of gels.