Gaseous abundances in planetary nebulae: What have we learned in the
  past five years?
  Nearly 50 years ago, in the proceedings of the first IAU symposium on
planetary nebulae, Lawrence H. Aller and Stanley J. Czyzak said that "the
problem of determination of the chemical compositions of planetary and other
gaseous nebulae constitutes one of the most exasperating problems in
astrophysics". Although the situation has greatly improved over the years, many
important problems are still open and new questions have arrived to the field,
which still is an active field of study. Here I will review some of the main
aspects related to the determination of gaseous abundances in PNe and some
relevant results derived in the last five years, since the last IAU symposium
on PNe.
