This book reviews recent results on low-dimensional quantum field
theories and their connection with quantum group theory and the theory
of braided, balanced tensor categories. It presents detailed,
mathematically precise introductions to these subjects and then
continues with new results. Among the main results are a detailed
analysis of the representation theory of U (sl ), for q a primitive root
of unity, and a semi-simple quotient thereof, a classfication of braided
tensor categories generated by an object of q-dimension less than two,
and an application of these results to the theory of sectors in
algebraic quantum field theory. This clarifies the notion of "quantized
symmetries" in quantum fieldtheory. The reader is expected to be
familiar with basic notions and resultsin algebra. The book is intended
for research mathematicians, mathematical physicists and graduate
students.