In Discipline and Punish: The Birth of The Prison, by Michel Foucault; How is the work presented as a genealogical research project that reveals...

For Foucault,  a "genealogy" embeds philosophy within a context of history and political power. Philosophical concepts and constructs simply don't float in a timeless ether: they are constructed in a particular period of history in response to the needs of those in power. Foucault owes a debt to Nietzsche and Marx in this "historicizing" of philosophical thought.

In Discipline and Punish, Foucualt turns on its head the idea that we have "progressed" and become more humane in our treatment of prisoners. His book is genealogical because it moves through history as it looks at both people incarcerated for crime and for mental illness. In both, he sees a dangerous trend on the part of the state in the last few centuries. The state has gone from a medieval/Renaissance control of the body, represented by simply putting a person suffering from mental illness in chains (or leading a criminal to a scaffold) to an attempt to control a mentally unbalanced or criminally convicted person's mind. Controlling the body is what Foucault calls "punishment," whether enacted on a "madman" or a criminal--it is the state's visible display of power over the bodies of its citizens. It is tied to particular historical epochs and to monarchial power, where the "body" of the king represents the state's power. 

While we see chaining up the "insane" as barbaric, Foucault understood it as leaving an individual free in his mental state--free to be who is, a chaining of the body but not a chaining of the soul. In contrast, experiments that began in the late 18th century to force people into isolation to think about and learn to self-censor their thoughts is a much more powerful form of control than merey chaining or killing a body. Getting inside a person's mind attempts to own an individual, body and soul. It is not a sign of "progress." In fact, Foucualt argeus passionately, it is more barbaric than the chains. Foucault dwells in great detail on Bentham's proposed Panopticon, a prison designed to maximize surveillance and to convince the prisoner he is under constant surveillance. Knowing he may be watched all the time, the prisoner will constantly self-regulate his behavior. Getting the imprisoned to self-regulate and self-censor according to needs and desires of those in power is what Foucalt called "discipline." It is an invisible form of power. 

"Punishment" and "discipline" are genealogical because they are tied to particular periods of history and particular forms of state power that have gone from the visible displays of punishment to the invisible controls of discipline.