Some resources to help understand Simondon’s thought.
– ‘On the Mode of Existence of Technical Objects’: the first part of Simondon’s doctoral thesis (in scruffy and, I understand, outdated translation in need of renewal).
– VIDEO: Interview ‘On Mechanology’
– In partial form (‘The Technical Object as Such’) with English subtitles
– Full interview in French with English summaries, courtesy of Terence Blake (in 5 parts; links to next parts at top right of page)
– Some rumination on Simondon that gives the lay of the land in relation to his influence and mysteriously untranslated status can be found, briefly, in relation to his ‘Two Lessons on Animal and Man’ and, more extensively, from Brian Massumi.
– A collection of Simondon translations (notably ‘The Individual and its Physico-Biological Genesis’), some commentary, and a really useful vocabulary (see the post of 28 Nov) at Fractal Ontology.
– Muriel Combes’ ‘Gilbert Simondon and the Philosophy of the Transindividual’ (MIT Press site): a recently translated and comprehensive introduction to Simondon that gives Stiegler’s reading decidedly short shrift. Steven Shaviro’s notes on the book, with reference to Stiegler, can be found here.
Chris has helpfully given an introduction to the Combes book and excerpted some useful passages below.
The interior milieu is specific to organic beings, the psychic milieu is specific to subjects, or self-conscious organic beings (which obviously implies beings with a developing technology of thought, e.g. language) – the psychic milieu just is that development from the perspective of the individual (in the sense of isolable thing). Both these milieus develop from the exterior milieu as part of the inevitable complexification of beings (which I suspect is resonant with Stiegler’s notion of tendency). For example a memory of something can be understood, in Simondian terms, as an internalisation of the exterior milieu, in this case it would be a fold into (a complexification of) the psychic milieu specifically. It’s interesting that this leaves the concept of memory to be conceived of as being as active or passive as you like. An associated milieu is just the exterior milieu and the shares of the exterior milieu which constitute the interior and psychic milieus all considered from the perspective of the collective rather than the individual. Some quotes from Combes’ book on Simondon (any elisions in square brackets are my own):
The difference separating two domains such as the physical and the living is not one of substance, and these two domains are not opposed as ‘living matter and nonliving matter.’ Rather, the difference between them is that which distinguishes ‘a primary individuation in inert systems and a secondary individuation in living systems’ (IG, 149; IL, 151). What differentiates two domains, then, lies in the individuation giving birth to the individuals populating each domain. What does this mean? It means that we must conceive of biological individuation not as something that adds determinations to an already physically individuated being, but as a slowing down of physical individuation, as a bifurcation that operates prior to the physical level proper. It is by diving back into the level of the preindividual prior to physical individuation that the individuation of a living being begins: ‘Phenomena of a lower order of magnitude, which we call microphysical, are not in fact physical or vital, but prephysical and prevital; the purely physical, not alive, would only begin at a supermolecular scale; it is at this level that individuation brings forth the crystal or the mass of protoplasmic matter’ (IG, 149-150; IL, 151-152). [. . .] animal individuation ‘finds sustenance at the most primitive phase of plant individuation, retaining something prior to the development into an adult plant, and in particular the capacity of receiving information over a long period of time.’ (IG, 150; IL, 152). Between the physical and the vital, between the plant and the animal, we need not look for substantial differences that lend themselves to founding distinctions between genus and species, but rather for differences in speed in the process of their formation. What divides being into domains is ultimately nothing other than the rhythm of becoming, sometimes speeding through stages, sometimes slowing to resume individuation at the very beginning.
Such observations about the heterogeneity of individuating rhythms make it possible to speak about what constitutes the difference between ‘physical beings’ and ‘living beings.’ living individuals differ from physical individuals in that they add a second ‘perpetual individuation that is life itself’ to the first instantaneous individuation in which they arise as complements of a milieu (IG, 25; IL, 27). As such, a living being is not only a result but also, and more profoundly, a ‘theater of individuation’ (ibid.). In contrast to a crystal or electron, a living being is not content to be individuated to its limit, that is, to grow along its outer edge: ‘The living individual has … true interiority, because individuation takes place within it; the interior is constituting in the living individual, while only the limit is constituting in the physical individual, and what is topologically interior is genetically anterior. The living individual is contemporary to itself in all its elements, while the physical individual is not, comprising a past that is radically past, even when it is still in the process of growing’ (IG, 26; IL, 28). The physical individual does not comprise a true interiority, since its interiority is of the past insofar as it entails a process of sedimentation, whereas the living being does not cease individuating within itself, which is why it exists in the present. In addition to an exterior milieu, living beings possess an interior milieu, such that their existence appears as a perpetual putting into relation of the interior milieu and the exterior milieu, which relation the individual operates within itself. The living individual is capable both of relations orientated toward its interior (regeneration, as internal genesis, being a prime example) and of relations exterted toward the exterior, such as reproduction. [22-3]
But what does it mean to think the reality of psychic being and the collective without calling on new substances? It means showing that psychic individuation and collective individuation prolong vital individuation, that they are the continuation of it. As individuated beings, living beings spring from a first, biological individuation. But, as we have already begun to see, living beings only maintain their existence by perpetuating this first individuation from which they emerged through a series ofindividualizing individuations. This continuation of the first individuation is called individualization. In effect, a living being, ‘in order to exist, needs to be able to continue individualizing by resolving problems in the milieu surrounding it, which is its milieu’ (IPC, 126; IL, 264). In the analysis proposed by Simondon, perception, for instance, appears as an act of individuation operated by a living being to resolve a conflict into which it has entered with its milieu. In his view, to perceive is not primarily to grasp a form; rather it is the act taking place within an ensemble constituted by the relation between subject and world, through which a subject invents a form and thereby modifies its own structure and that of the object at the same time: we see only within a system in tension, of which we are a subensemble. [. . .] If we admit that psychic individuation consists of a series of individuations that prolong the first individuation of the living being, we will then conclude: ‘Each thought, each conceptual discovery, each surge of affection reprises the first individuation; thought develops as a reprise of this schema of the first individuation, of which it is a distant rebirth, partial but faithful’ (IPC, 127; IL, 264). [26-7]
it is more a question of psychic problems than a psychic individual. Only two sorts of individuals exist: physical individuals and living individuals. This is why, if we are to be rigorous, we must say that there ‘is not properly speaking a psychic individuation, but an individualization of the living being giving birth to the somatic and the psychic’ (IPC, 134; IL, 268; emphasis added). Psychic individuation is a perpetuation of vital individuation. 
Because machines know only givens and schemas of causality, it falls back on humans to establish correlations between machines. Although this may appear rather obvious (who would imagine that machines are capable of spontaneously connecting with one another?), this idea takes on new depth in Simondon’s version of it. It is as living beings that humans are declared responsible for technical beings, that is, insofar as they are inscribed in time, and as a result, have the capacity to act retroactively on their life conditions by modifying the forms of problems to be resolved. We should recall that it is, in fact, in temporal terms that Simondon explains the capacity to invent, which in his view characterizes living being as a theatre of individuation: invention, as the act of a living being ‘bearing its associated milieu with it,’ is described as ‘an influence of the future on the present, the virtual on the actual’ (MEOT, 58). Thus we might say that the human plays the role of transducer between machines; humans ‘assure the function of the present, maintaining the correlation, because their life is made of the rhythm of the machines surrounding them, which they link together’ (MEOT, 126) 
Abbreviations for source texts in the above:
IG: L’individu et sa genese physico-biologique, Presses Universitaires de France, 1964; Editions Jerome Millon, 1995.
IPC: L’individuation psychique et collective, Aubier, 1989.
IL: L’individuation a la lumiere des notions de forme et d’information, Editions Jerome Millon, 1995. (combines IG and IPC, and is now the standard edition)
MEOT: Du mode d’existence des objets techniques, Aubier, 1958, 1969, 1989.