Spectroscopy of atomic hydrogen. How is the Rydberg constant determined?
  This article presents a review of the most recent theoretical and experimental results in hydrogen. We particularly emphasize the methods used to deduce the Rydberg constant $R_\infty$ and we consider the prospects for future improvements in the precision of $R_\infty$. 
Fran\c{c}ois Biraben (LKB - Jussieu, LSH-ENS)