In 1927, Frederic Thrasher observed that “No two gangs are just alike” (1927, 45). Of course, the point of Thrasher’s emphasis was heuristic; it directed attention to the diversity within gangs identified in his fieldwork in Chicago. This chapter is motivated by Thrasher’s early observations and uses data from the LoneStar Project to examine this claim quantitatively with application to prisons. If gangs are not all alike, in what ways are they different? If they are indeed different, what explains the differences and similarities across gangs? And, most importantly, what role does prison play in explaining variation in the group-level characteristics of prison gangs? While these questions guide our interests in this chapter, our overarching goal is to describe the characteristics of gangs in prison.