How do they recruit? I can't really find anything on the subject.

As a slightly related note:

Would it be remotely plausible for a technologically-inclined Guardsman to get inducted into the Cult (as a low-ranking Adept) if, say, a Tech-Priest took interest and vouched for them?

The Adeptus Mechanicus, much like the Space Marines and the Ecclesiarchy, are granted their own domains in the form of Forge Worlds to reign over as they see fit. These planets are not only their centers of industry and worship, but of course also recruiting grounds for the priesthood, the servitors, and of course the Tech-Guard aka Skitarii.

Details to how this recruitment functions are flimsy to non-existent, but personally, I like the idea put forward in the DH1 core rulebook where the authors suggest that recruitment on Forge Worlds is based on nothing more than chance, as each inhabitant is merely a number for the administration -- so if it's time to recruit another batch of, say, Skitarii, they simply send summons to citizens #34B-8843000 to #34B-8845999 to report for induction. Suitably grimdark and a nice representation of a Forge World truly being the embodiment of a "well oiled machine", with every human subject being nothing but a tiny cog.

That's not to say that a Tech-Priest may not spot a talented worker in a manufactorum and raise them into the priesthood, of course.

Would it be remotely plausible for a technologically-inclined Guardsman to get inducted into the Cult (as a low-ranking Adept) if, say, a Tech-Priest took interest and vouched for them?

Ehhh ...

Well, I guess it should be remembered that 40k doesn't actually have much in the way of a uniform canon. There are numerous conflicts between the official sources, so you'd be absolutely entitled to your own little deviations. I'd still caution to find a way to make it "fit in", though, as this would increase the likelihood of your group condoning such things.

For example, an opportunity I could see here would be one of the regiment's accompanying Enginseers noticing this Guardsman's aptitude for working with machinery, and - since they just lost a bunch of their own people - enlisting him to help out as a sort of Astech, an assistant. The AdMech envoy would talk to his or her commanding officer and arrange for this special duty to replace other menial tasks the soldier would otherwise have to carry out whilst encamped (such as cleaning).

And then just have things develop from there? Mind you, it should not represent an official sanction right away, but rather the start of a relationship and exposure that may at some point result in the Guardsman's "patron" contacting a Forge World to inquire about the possibility of a transfer of this assistant under the Cult Mechanicus' care, thus making things official.

Imagine the Freemasons if they controlled all knowledge on how technology worked, but were much, much more secretive about how they operated and recruited than they are in the real world. That almost approaches how I see the Adeptus Mechanicus.

So that's about how I would approach getting into the AM or what sort of information the PCs know about the organization: nothing.

Keep in mind, too, that the Mechanicus views Guardsmen as less valuable than the lasguns they carry. Tech-Priests should probably be shown as contemptible of the PCs at best, and outright ignoring them at worst.

A guardsman is part of an entirely different nation, practically, than the AdMech. A guardsman who helps out the AdMech might get something approaching 'honorary citizenship' in terms of something like the Cog of Het, and in such cases they might be accepting of said Guardsman hanging out with them, and visiting their worlds, but he's not really in line to become a member of the priesthood.

One other method of recruiting that is mentioned in the AdMech codex is that Skitarii who distinguish themselves may become inducted into the priesthood. I imagine it's like a combination of social caste and going to college in a society with intense income stratification - parents would do anything to get their kids into the priesthood, and once you're there you kind of look down on the rest of the plebs. And it probably has ridiculously intense entrance exams etc.

I always thought that, given the lack of social skills among the AM, there is some sort of machines that choose whether one should become a tech-priest. Maybe they're archeotech devices that can scan infant's genome and brain in search of genes and neuron structures that may give them analytical mind, natural curiosity, reasonable disposition and other things like that.

That would make sense for me, given AM's distrust in human flesh and their faith in wisdom of the ancients and their machines.

On the other hand, as they love rituals and celebrate them despite not knowing their true meaning, there could be a whole bunch of "quests" that a candidate must complete to become a tech-priest. Some of them might be completed even before he became one! Others might be things so trivial and silly like stamping a letter 100 times in a row.

Anyway, AM are not normal people, so they shouldn't recruit like them.

Based off of the AdMech's *inability* to buy up Fellowship or Fellowship-related skills in earlier versions of this rpg system, the argument has been made that Logic should be an acceptable skill to be able to be used for social interactions with the dudes in red. Personally, I don't think that should hold true, on account of their penchant for ritual and superstition making them every bit as illogical as anyone else in the zany 40k universe, but I see the argument. So in that case I could see it not being something that involves politicking or social status the way we understand it. But I work in research science, and for all the public sees it as a bunch of eggheads sitting around being logical, it's as much about social skills, grudges, attractiveness, and all that stuff as any other job. So, to me, it makes sense that people outside would see them as coldly logical in this way, especially because most outsiders don't speak Techna-Lingua or communicate via cybernetic radios, but all the same bull is actually present there.

Yeah, you still have AdMech run intrigues against one another, trying to one-up another, and so on. If they were all about logic, they would not have kicked off a civil war over whether to accept the Emperor's rule or not.

"The lowest ranks of Techpriest have mainly maintenance and construction duties, but as a Tech-adept progresses and acquires greater knowledge, he is relieved from day to day tasks to study ancient texts and learn the greatest mysteries and techniques. Thus, the Adeptus Mechanicus endeavours to maintain this position of absolute knowledge and authority, and a Techpriest who feels that this is threatened will go to any lengths to protect his power, including murder, extortion, kidnapping, sabotage and terrorism."

-- GW d100 Inquisitor

Of course, that does not preclude an automatic selection system -- one might say that the Tech-Priests are well aware of their own weaknesses (as they are still "part flesh"), and thus only really trust the ostensibly neutral machine spirit/s whenever possible.