  Great strides have been made in the understanding of bound states of a bottom
quark $b$ and its antiquark $\bar b$ since the discovery of the first
$\Upsilon$ resonances in 1977. These {\it bottomonium} bound states have a rich
spectrum whose masses and transition amplitudes shed valuable light on the
strong interactions. The present article reviews some recent developments in
bottomonium physics. These include the discovery of the spin-singlet states
$\eta_b$ and $h_b$, the first D-wave states, one or more candidates for
spin-triplet $\chi_b(3P)$ excitations, and above-threshold states with strong
transitions to states below threshold. Information on transitions, production,
and signatures of new physics is also presented.
