Some additions to Andara's writeup:
The first five "XXXenophile Collection" books reprinted stories from the first ten issues of the comic series; however, there isn't a two-to-one correlation between them (collection 1 is not comics 1 plus 2, it's got two stories from each of issues 4 and 9, and one story from each of 1, 2, 3, and 7, if I've counted right.). Each collection also had one new story, not previously seen in the comic series. These new stories were later collected into issue 11 of the comic series. So in some ways 11 was an afterthought, and I'm not surprised that the XXXenophile web site has sections that were either written before it was published or overlook it. Regardless, you can either go the 11 comics route or the 5 collections route and get all the stories; you get more covers and letter pages and bios of the inkers and so forth with the comics though. (Collection 6 is a completely new, full length single story, with no corresponding comic series entry.)
Phil Foglio wrote and pencilled every story, but different inkers did the finishing work on the art on each story; I don't think there are any repeat appearances by inkers until Collection 6. If there's no other reason that the series is interesting, it is a demonstration of the effect that the inker, in many ways the unsung hero of the comic art form, has on the look of the final product. (Well, colorists are more unsung than inkers, but all of XXXenophile is black and white, so no songs for them here. And letterers don't get sung about much either...)
Phil Foglio's current work is the steampunk comic Girl Genius.