This book presents a self-contained introduction to H.M. Stark's remarkable conjectures about the leading term of the Taylor expansion of Artin's L-functions at s=0. These conjectures can be viewed as a vast generalization of Dirichlet's class number formula and Kronecker's limit formula. They provide an unexpected contribution to Hilbert's 12^th problem on the generalization of class fields by the values of transcendental functions. This volume belongs on the shelf of every mathematics library.