Stellar Populations
  This is a summary of my lectures during the 2011 IAC Winter School in Puerto
de la Cruz. I give an introduction to the field of stellar populations in
galaxies, and highlight some new results. Since the title of the Winter School
was {\it Secular Evolution of Galaxies} I mostly concentrate on nearby
galaxies, which are best suited to study this theme. Of course, the
understanding of stellar populations is intimately connected to understanding
the formation and evolution of galaxies, one of the great outstanding problems
of astronomy. We are currently in a situation where very large observational
advances have been made in recent years. Galaxies have been detected up to a
redshift of 10. A huge effort has to be made so that stellar population theory
can catch up with observations. Since most galaxies are far away, information
about them has to come from stellar population synthesis of integrated light.
Here I will discuss how stellar evolution theory, together with observations in
our Milky Way and Local Group, are used as building blocks to analyze these
integrated stellar populations.
