The concept of a biorefinery that provides valuable bioproducts from biomass conversion instead of fossil based products is presented. One of the main biorefinery products, bioethanol, can be produced from sugar, starch, or lignocellulosic-based biomass. Lignocellulosic-based bioethanol could be a good alternative to sugar- or starch-based bioethanol. While sugar- and starch-based biomass includes mainly glucose or starch, lignocellulosic biomass contains cellulose, hemicellulose, and lignin. While the cellulose is essential for the biomass-to-bioethanol conversion process, hemicellulose and lignin are undesirable in this context, and therefore pretreatment is necessary to break down the lignocellulose structure and separate hemicellulose and lignin from cellulose. Organosolv pretreatment is an attractive method for separating both cellulose and nearly pure lignin from the lignocellulosic material. In a biorefinery, organosolv pretreatment is one of the best options for producing more than one valuable product (bioethanol and lignin) in the same process. For effective bioethanol production, the delignification rate and enzymatic glucose conversion are fundamental parameters. This paper presents a detailed literature review of organosolv pretreatment, focusing on the effects of each of the pretreatment conditions for biorefinery applications. The organosolv pretreatment method is first described in detail and then each of the pretreatment conditions is explored individually. A number of technical studies are reviewed, and the effects of the various conditions on the delignification rate and on enzymatic glucose conversion for effective bioethanol production are described. The current status of development of organosolv-based biorefineries around the world is discussed. In previous reviews of this topic, only the solvent and catalyst effects have been investigated. This review will contribute to the literature by showing the impacts of all pretreatment conditions on pretreatment efficiency. Published by AIP Publishing.