The FIRST Lego League (also known by the acronym FLL) is an international competition for elementary and middle school students (ages 9-14 in the USA and Canada, 9-16 elsewhere). It is arranged by the FIRST organization.
Each year the contest focuses on a different real-world topic related to the sciences. Each challenge within the competition then revolves around that theme. The robotics part of the competition revolves around designing and programming LEGO Robots (either RCX or NXT to complete tasks. The students work out solutions to the various problems they are given and then meet for regional tournaments to share their knowledge, compare ideas, and display their robots.
FIRST LEGO League is a partnership between FIRST and The LEGO Group. It also has a scaled-down robotics program for children ages 6-9 called Junior FIRST LEGO League.