The discoveries and subsequent developments within the field of metamaterials have opened up for novel light-matter interactions towards the engineering of light behavior. The astonishing phenomenon of negative refraction remains challenging to realize for visible frequencies, and non-magnetic gain metamaterials have been proposed towards this end. This thesis pursues this idea by presenting a conceptual framework for which to understand the requirements and possibilities emerging from the causal behavior of the dielectric response. This results in clear and concrete instructions on how the dielectric response must be designed towards negative refraction. These are offered in terms of a novel perspective employing zero- and pole placements in rational functions and analysis of the dielectric function in its complex plane. A number of negative index systems are evaluated including two component media and low gain negative index media. Negative index concepts are introduced to the Electromagnetically Induced Transparency system. A strategy towards design and realization of arbitrary dielectric responses in terms of Krein and Nudel'man causal extrapolation is also presented.