2 John
See 
Authorship
Both 2 John and 3 John are attested later than 1 John because they were too brief to be cited often by early church fathers. Usually letters of this length are too brief for stylistic comparison. Nevertheless, the style (as well as the theology) is close to that of 1 John, and this points to common authorship of the three letters.
Genre
Both 2 John and 3 John are letters. Unlike most NT letters, 2 and 3 John are both the length of most surviving ancient letters. The average ancient letter required only a single sheet of papyrus.
Background
Second John addresses the same central error that 1 John addressed (see 
Quick Glance
The apostle John
Audience:
The “lady chosen by God,” probably a local church in western Asia Minor
Date:
Between AD 85 and 95
Theme:
John writes to urge discernment in supporting traveling teachers, since false teachers were also traveling and teaching heresy.
