  We give an overview of recent experiments on an ultracold Fermi-Bose quantum
gas where the interspecies interaction can be tuned via magnetic Feshbach
resonances. We first describe the various steps that have led to the
observation of Feshbach resonances in the K-Rb system we investigate, and their
accurate characterization. We then describe experiments in which Feshbach
resonances are exploited to study interaction effects and to associate weakly
bound KRb dimers.
