I want to read the K Project manga, but there are a lot of series. So what's the order for these series?
If you mean publication order, the K wikipedia article's manga section doesn't list all the publication dates, but seems to list them in publication order.
By serialization publication start date (end date included if applicable/known):
- 2012 ? (no later than November) - 2013 ? (tankobon release 2013 April): K Stray Dog Story
- 2012 May - 2013 July: K -Memory of Red-
- 2013 October - 2014 July: K -Days of Blue-
- 2013 December - 2015 April: K - The First
- 2014 January: Gakuen K
- 2014 June: K: Lost small world
- 2014 December - 2015 July: K: Countdown
- 2015 April - August: K: Missing Kings
- 2015 May - November: K: Dog and Cat
- 2015 September: K: Dream of Green
- 2015 October: K: Return of Kings
Based on the various summaries and news articles, I've placed them in approximate chronological order (some of the stories overlap) using the anime series as a guideline.
Before K TV
- K: Lost small world
- K -Memory of Red-
- K -Days of Blue-
- K: Stray Dog Story
Adaptation of K TV
- K - The First
After K TV / Before Movie
- K: Dog and Cat
Adaptation of K Movie
- K: Missing Kings
After Movie / Before K TV2
- K: Countdown
Before and/or Overlaps with K TV2?
- K: Dream of Green
Adaptation of K TV2
- K: Return of Kings
- Gakuen K (comedy spin-off where all characters attend high school together)