Geodesic flows of Riemannian metrics on manifolds are one of the
classical objects in geometry. A particular place among them is occupied
by integrable geodesic flows. We consider them in the context of the
general theory of integrable Hamiltonian systems, and in particular,
from the viewpoint of a new topological classification theory, which was
recently developed for integrable Hamiltonian systems with two degrees
of freedom. As a result, we will see that such a new approach is very
useful for a deeper understanding of the topology and geometry of
integrable geodesic flows. The main object to be studied in our paper is
the class of integrable geodesic flows on two-dimensional surfaces.
There are many such flows on surfaces of small genus, in particular, on
the sphere and torus. On the contrary, on surfaces of genus 9 > 1, no
such flows exist in the analytical case. One of the most important and
interesting problems consists in the classification of integrable flows
up to different equivalence relations such as (1) an isometry, (2) the
Liouville equivalence, (3) the trajectory equivalence (smooth and
continuous), and (4) the geodesic equivalence. In recent years, a new
technique was developed, which gives, in particular, a possibility to
classify integrable geodesic flows up to these kinds of equivalences.
This technique is presented in our paper, together with various
applications. The first part of our book, namely, Chaps.