I'm teaching a Foucault seminar this term (hence the recent flurry of posts on the prison-industrial complex). In prepping the course I re-read this passage I wrote a few years ago (from this article) which claims a close connection between Foucualt's methodology and Deleuze's notion of "multiplicty."
In Security, Territory, Population, Foucault tells us to avoid a "circular ontology of the state" (STP 362F / 354E); we have to keep from hypostasizing the state as a substance, and avoid what Foucault will call "state phobia." In an important passage in Birth of Biopolitics Foucault concentrates on the "statification" [étatisation] of governmental practices. But this does not mean analyzing the "essence" of the state and then trying to deduce current practices of state governmentality as accidents accruing to the substance defined by that essence. For Foucault, flatly stated, "the state does not have an essence"; it is not "an autonomous source of power" (NB 79F / 77E). Rather it is only the "effect, the profile, the mobile shape [découpe mobile] of a perpetual statification [étatisation] or perpetual statifications [étatisations] in the sense of incessant transactions which modify, or move, or drastically change, or insidiously shift" multiple practices such as finance, investment, decision-making, control, and relations of local / central authorities (NB 79F / 77E). The state has no essence; it is not a substance with changing properties, but what Deleuze would call an Idea, a multiplicity, a system of differential elements and relations involved in "incessant transactions."[i]
[i] With "incessant transactions" we have a strong echo of the Deleuzean notion of a multiplicity as a structure of continuous variation. Relatively low-key in Difference and Repetition (e.g., 326F / 253E), continuous variation is a major concept throughout A Thousand Plateaus.