The fine tuning of thioglycosides used as glycosyl donors occurs through careful manipulations of the aglycon's nucleofugality, for example, by using "active-latent" principles. In the first section, the control of the relative leaving group abilities will be discussed in terms of electronic factors, including electron-donating/withdrawing substituents. In the second section, the nucleofugality will be adjusted by steric factors. Quantitative reactivity relationships will then be documented followed by presentation of other controlling elements including locked conformations, solvents, and promoters that will be illustrated throughout.