  We present the Mathematica application LieART (Lie Algebras and
Representation Theory) for computations frequently encountered in Lie Algebras
and representation theory, such as tensor product decomposition and subalgebra
branching of irreducible representations. LieART can handle all classical and
exceptional Lie algebras. It computes root systems of Lie algebras, weight
systems and several other properties of irreducible representations. LieART's
user interface has been created with a strong focus on usability and thus
allows the input of irreducible representations via their dimensional name,
while the output is in the textbook style used in most particle-physics
publications. The unique Dynkin labels of irreducible representations are used
internally and can also be used for input and output. LieART exploits the Weyl
reflection group for most of the calculations, resulting in fast computations
and a low memory consumption. Extensive tables of properties, tensor products
and branching rules of irreducible representations are included in the
appendix.
