The Fast Multipole Method (FMM) was named one of ten “algorithms with the greatest influence on the development and practice of science and engineering in the 20th century” in Computing in Science & Engineering (Jan/Feb 2000). Its inventors Rokhlin and Greengard won the 2001 AMS Steele prize. Is there anything left to say after more than 1000 papers devoted to fast numerical solutions of Poisson's equation? Comparitively less attention has been devoted to the FMM with periodic boundary conditions, a problem central to computational astronomy, chemistry, and biology. I will discuss some of the finer points of efficiently implementing the FMM, in particular a technique for extending the FMM to periodic boundary conditions.