  This is a report on some highlights of some research on the rare light
elements, lithium (Li), beryllium (Be), and boron (B), that I presented in my
Henry Norris Russell Lecture in January, 2020. It is not a comprehensive review
of work on these light elements, but contains sections on Big Bang
nucleosynthesis of Li and the rarity of these light elements. It includes
information on how they are observed, both historically and currently, and the
difficulties entailed in determining their abundances. %It traces the evolution
of these elements through the history of the Galaxy. The production of Li, Be,
and B is ongoing so the youngest stars contain the most Li, and they have had
less time to destroy it. All three elements are readily destroyed in stellar
interiors, but have differing degrees of susceptibility to the particular
nuclear fusion reactions which deplete their surface content. This feature
makes them remarkably good probes into the otherwise unobservable interiors of
stars. It also enhances the use of two or more of the three in sorting out the
various processes at work in the insides of stars.
