Quasi-zero stiffness （QZS） vibration isolation， by introducing stiffness nonlinearity， effectively addresses the inherent contradiction between load-bearing capacity and isolation bandwidth in conventional linear isolators. As a result， it exhibits superior low-frequency isolation performance. The core challenge in realizing QZS isolation lies in designing mechanical structures whose force-displacement curves simultaneously demonstrate high static stiffness and low dynamic stiffness. Focusing on QZS isolation design methodologies， this paper first outlines the fundamental principles of QZS isolation and categorizes the traditional approaches according to the means of stiffness nonlinearization into four groups： geometric motion nonlinearity， geometric deformation nonlinearity， magnetic nonlinearity， and stress-strain nonlinearity. Subsequently， it introduces emerging design strategies based on nonlinear positive-stiffness structures， including hardening and softening types， and compares them with conventional approaches， with particular attention to their differences in static and dynamic behavior. Finally， the paper summarizes and discusses future directions from the perspectives of negative-stiffness structure design， QZS characteristic tuning， and potential applications， aiming to provide a comprehensive overview of the latest research progress and to offer insights into future development trends of QZS isolation systems.