The term diet quality has recently gained considerable attention in nutritional research. Despite widespread use, it is often poorly defined and remains difficult to measure. Confusion surrounds the term, as there is no consensus on how to define quality of the diet or to pin down a framework for producing a standard indicator. The composite and cut-off selection of most diet quality indices depend on investigator choices in line with research objectives. In addition to the frequently used dietary compliance-based approach, innovative approaches have emerged to construct diet quality indices based on antioxidant and anti-inflammatory profiles of diet. Different viewpoints and overlapping interests may yield different interpretations. Most of the unresolved issues are related directly or indirectly to the multidimensional and open-textured nature of the concept.