In this expository text we sketch some interrelations between several
famous conjectures in number theory and algebraic geometry that have
intrigued math- ematicians for a long period of time. Starting from
Fermat's Last Theorem one is naturally led to introduce L- functions,
the main, motivation being the calculation of class numbers. In partic-
ular, Kummer showed that the class numbers of cyclotomic fields play a
decisive role in the corroboration of Fermat's Last Theorem for a large
class of exponents. Before Kummer, Dirichlet had already successfully
applied his L-functions to the proof of the theorem on arithmetic
progressions. Another prominent appearance of an L-function is Riemann's
paper where the now famous Riemann Hypothesis was stated. In short,
nineteenth century number theory showed that much, if not all, of number
theory is reflected by properties of L-functions. Twentieth century
number theory, class field theory and algebraic geome- try only
strengthen the nineteenth century number theorists's view. We just
mention the work of E. H cke, E. Artin, A. Weil and A. Grothendieck with
his collaborators. Heeke generalized Dirichlet's L-functions to obtain
results on the distribution of primes in number fields. Artin introduced
his L-functions as a non-abelian generalization of Dirichlet's
L-functions with a generalization of class field theory to non-abelian
Galois extensions of number fields in mind.