Résumé : The course will explore several related topics in number theory with dynamical and/or geometric facets: continued fractions, Diophantine approximation, and Apollonian circle packings. We will focus on both theoretical and experimental tools, a parallel goal will be to experience the role of visualization and illustration in mathematical research. In covering background material, the approach will emphasize the visual and dynamical:
(1) Continued fractions, quadratic forms, and Diophantine approximation.
(2) Hyperbolic geometry, Minkowski space, and Kleinian groups.
With these tools at hand, we will study some areas of current research:
(1) The geometry of Diophantine approximation and continued fractions in the complex plane,including algebraic starscapes and Schmidt arrangements.
(2) Apollonian circle packings, with an emphasis on their surprising relationships to the preceding topics.

Keywords : continued fractions; Apollonian circle packings; Diophantine approximation; Kleinian groups