This paper presents a novel concept for the isolation of vibrations using magnetically adjusted springs in conjunction with a feedback regulation system. At the heart of the system proposed is a nonlinear magnetic spring component, the constitutive properties of which enable it to passively achieve negative stiffness over a limited region of displacement. When mounted in parallel with a conventional, linear spring, the result is a nonlinear spring with a nearly flat constitutive curve for a certain displacement range. Within this range, therefore, the spring behaves as though it were extremely soft, thereby passively affording the desirable isolation characteristics associated with a soft spring, only without the inherent physical disadvantages. A simple feedback regulator is necessary in order to insure that the system operates within its linear range. The paper presents some background to the problem of vibration isolation and then discusses the fundamental design and operation of the magnetic springs. Next, we propose a simple PI controller for operating-point regulation and maintenance of linear operation. Following an analysis of predicted spring performance, we then present a numerical simulation of the entire system and compare this result to that obtained from experiments performed with a laboratory prototype.