Ultracold Fermi gases near a Feshbach resonance allow one to realize a crossover from a BCS-type superfluid to aBose-Einstein-Condensate of strongly bound pairs. I will discuss the thermodynamics of this crossover, emphasizing the universal behavior at infinite scattering length. A microscopic signature of pairing is provided by radiofrequency-spectroscopy. The average clock-shift is a measure of the pair-interaction energy which, however,hardly changes between the superfluid and a normal state reached beyond a critical spin-imbalance. Understandingthe phase diagram and excitation spectrum of imbalanced gases still provides a challenge for both theory and experiment.