This paper lays out fundamental social and economic principles that must be addressed in order to enable true High-Performance Computing resources sharing at the scale of a national Grid. Focusing on the literature around the concept of a Grid Economy, it starts by a rather exhaustive survey of related work in utility computing, market-based scheduling and other economic approaches in resource allocation. Building on forces and weaknesses of previous work, high-level principles to be followed to establish a sustainable and pervasive Grid sharing framework are detailed.