The primary structural difference between modafinil (trade name Provigil) and armodafinil is that armoda (r-moda) is the dextro-rotary or "right handed" version of the molecule as opposed racemic (s-isomer AND dextro-rotary/r-isomer) mixture of enantiomers. Off the bat, this does a few things. First off, the r-isomer is more psychoactive than the l-isomer so many folks report armodafinil being more psychoactive, it also often has a stronger kick and lasts a tad longer. Armodafinil is known by the trade name Nuvigil. Armodafinil and other analogues are often easier to get a hold of than prescription Provigil (racemic modafinil). The modafinil generics Waklert, Artvigil, R-Modawake are generally r-isomer modafinil. Another very important difference is that armodafinil is more potent by the milligram. Due to it's being more psychoactive some find it has more of a mood-boosting effect. In case you weren't aware, in addition to narcolepsy, studies have been done on the potentiality of modafinil (and its analogues) in treating clinical depression, ADD/ADHD and other conditions. Another thing to consider here though is the fact that for those who are stimulant sensitive or who feel modafinil is too "pushy" armodafinil may have a tendency to be anxiety-inducing. Probably my favorite form of moda.