Abstract: What are the effects of deliberation about legal and political issues by like-minded people? This Essay reports the results of an experimental investigation involving sixty-three citizens in Colorado. Groups from Boulder, a predominantly liberal city, met to discuss global warming, affirmative action, and civil unions for same-sex couples. Groups from Colorado Springs, a predominately conservative city, discussed the same issues. The major effect of deliberation was to make group members more extreme in their views than they were before they started to talk. Liberals became more liberal on all three issues; conservatives became more conservative. As a result of intra group deliberation, the division between the citizens of Boulder and the citizens of Colorado Springs significantly increased. Deliberation also increased consensus and significantly reduced diversity within the groups. Even anonymous statements of personal opinion became more extreme and less diverse after deliberation. Because political views are often distributed along geographical lines, these findings are highly likely to be replicated in actual deliberative processes unless safeguards and careful procedures are introduced.