This chapter describes five working theories that can be useful to practicing community psychologists. They are the brain children of David McMillan in collaboration with others including J. R. Newbrough and Ray Lorion. The five theories are: 1. A four major-element, twenty-six sub-element theory of Psychological Sense of Community; 2. A four-part typology of communities building on Tönnies 1800’s two types of community, Gemeinschaft and Gesellschaft – McMillan adds two additional types, Gefolgschaft and Notschaft; 3. Community moods: McMillan proposes that emotions are contagious. He offers nine basic emotions common to humankind and proposes that these emotions can function like a virus and can be treated similarly with emotion antidotes; 4. Communities have developmental stages: McMillan builds on Erikson’s (1968) eight stages of human development and adds two other stages, conception and termination; 5. The last practical theory McMillan offers is Newbrough’s (1995) Third Position Theory. This theory creates a negotiation, mediating problem-solving strategy that can undo dichotomous gridlock.