In recent years, product quality has become more and more important, due to consumer concerns paired with well-being and a healthy lifestyle. Product quality is a complex, multidimensional and multi-factorial issue that relates to different factors. In this chapter, the objective, measurable and intrinsic aspects of quality related to the reaction of greenhouse plants to several environmental and pre-harvest factors is outlined. With reference to studies carried out from the beginning of this century, the effects of such factors on visual, organoleptic and nutritional product quality properties are presented. The main factors influencing the quality of produce are covered, these include assessing the impact of light, temperature, air humidity, carbon dioxide enrichment, root environment and growing techniques and cultural practices. The degree of produce maturity and ripeness at harvest is also discussed. The chapter concludes with a look towards future trends in research.