This book considers the question how complex systems suddenly emergeduring the course of evolution and why the long-winded evolution ofsystems and species is interspersed with short phases of fast revolutions.Based on an agent based view of complex systems, the author gives wellillustrated explanations for the emergence of complexity and describeshow systems become more and more complex. From ancient cultures tomodern states and from the earliest primitive organisms to self-conscioushuman beings, the text explores the widest range of phenomena with thefewest possible principles.All Multi-Agent Systems have a natural system boundary, the agent itself.As the word "emergence" suggests, the emergence of complexity is alwayspossible at system boundaries, which enable the transfer of complexitybetween different systems. Fitness barriers set the boundaries of evolution.Revolutions in evolution are possible because evolution gets stuck from timeto time when a large fitness barrier is reached. Evolution waits until massivecatastrophes break these barriers or single agents are able to cross themthrough a tunneling process.