  In these notes we review emergent phenomena in complex systems, emphasizing
ways to identify potential underlying universal mechanisms that generates
complexity. The discussion is centered around the emergence of collective
behavior in dynamical systems when they are poised near a critical point of a
phase transition, either by tuning or by self-organization. We then argue the
rationale for our proposal that the brain is naturally poised near criticality
reviewing recent results as well as the implications of this view of the
functioning brain.
