Prevelo bikes come almost fully assembled. Here are the complete assembly requirements for each bike:

Alpha Zero: (1) attach handlebar to steerer tube and (2) adjust seat height

14" and 16" bikes: (1) attach handlebar to stem, (2) attach pedals and (3) adjust seat height

20", 24" and 26" bikes: (1) attach handlebar to stem, (2) attach front wheels, (3) attach pedals and (4) adjust seat height

You can view assembly instructions for all bikes here: