Plants are unique among multicellular organisms in that they can maintain growth of new tissues and organs throughout their lifetimes – in some species, over the course of hundreds or thousands of years. This remarkable ability derives from a population of self-renewing cells in the growing tip, known as the apical meristem. The maintenance of this cell reservoir is controlled genetically, and recent studies using the laboratory model organism Arabidopsis have begun to shed light on the mechanisms by which plants grow and develop over extended periods.