This web site by Donelson Forsyth presents a thorough analysis of why we form into groups, what needs they satisfy, and what functions they perform. (
http://www.has.vcu.edu/psy/faculty/fors/fun97.htm
)
This web site for the Center for Leadership Studies contains the findings of recent studies on the social psychological dynamics of leaders as instruments of change within a group. (
http://www.situational.com/
)