User blog comment:B214/Question & Answers 5/@comment-26200890-20160210195437/@comment-26345952-20160210223114

There is no special order to read them, you can read as they are numbered.

The DX series is compilation of short  stories, much like vol 8 and vol 13, that have apperead through the serialization of the LN. In my opinion, is best to read it after vol 19.

The DxD EX series is side story of the future children of Issei coming to the past and prevent any dangerous alteration in story. Though you can live without reading it; it's not important to the main story but you can say is sort of cannon. Read at your discretion.

If you wish more of the LN keep going around the wiki, wether its story, characters, teminology or anything in particular we have the answers.