"Lie Groups Beyond an Introduction, Second Edition", takes the reader from the end of introductory Lie group theory to the threshold of infinite-dimensional group representations. Merging algebra and analysis throughout, the author uses Lie-theoretic methods to develop a beautiful theory having wide applications in mathematics and physics. New to the second edition, apart from revisions and updates throughout, are chapters on branching theorems and prehomogeneous vector spaces, topics of interest to mathematicians and physicists alike.