Each year in August,  FIRST LEGO League introduces a scientific and real-world challenge for teams to focus and research on.  The robotics part of the competition involves desigining and programming Lego Mindstorms robots 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.
The competition is split into three judged sections and a live robot run. The first judging session, Core Values ,  is designed to detect how the team works together and uses the FLL Core Values, which include teamwork, Gracious Professionalism , and Coopertition . Teams are also asked to perform a teamwork exercise (usually timed). Secondly, in the Robot Design , or technical judging,  the team explains how they designed their robot and demonstrates their programs to the judges. Thirdly, in the Project ,  the students must research a topic related to the current challenge and create an innovative solution. The teams have 5 minutes to present their ideas, and the judges have another 5 minutes to ask questions. Finally, the students must use the robots they designed and built to autonomously complete a set of tasks on the challenge mat.
The robots made by the teams perform at this event. The robot is autonomous  and completes missions on a mat or board (where the missions are set up). The robot then has two and a half minutes to complete those missions. Two members of the team are allowed at the board during a match; however, they can switch out if needed. In the case of a serious problem, such as the entire robot breaking down, the entire team is allowed at the board for as long as the problem persists. Only one robot is allowed per team at the table; otherwise the team is disqualified. Members are not permitted to bring board items from other practice tables to the board during competition
The robot starts in an area marked as 'base'. This is a white area in the corner or to one side of the table. In base, two team members are allowed to touch the robot and start programs. If the team touches the robot while it is outside of base (a 'rescue' or 'retrieve'), the touch penalty objects are removed from play. These are mission models that are worth points without manipulation, providing an incentive to not rescue the robot. The robot is not required to return to base; some teams have completed all their missions without returning to base during the time allowed to complete the missions. In fact, in the 2008-09,  2009-10,  2011-2012, and 2012-13 challenges, points were awarded if the robot was in one of two specified areas, not including base, at the end of the two and a half minute match.
FIRST Lego League teams use Lego Mindstorms  kits to construct their robots. The robots are programmed using one of the block-based programing environments: the official EV3 software, the official NXT-G software (now outdated), or Robolab . All these are built around Labview . The team is currently allowed to bring a maximum of 4 motors to the table for each match.
Teams in different parts of the world have different times allotted to complete the construction of the robot, due to the varying date of qualifying tournaments. They go on to compete in FLL tournaments, similar to the FIRST Robotics Competition regionals. In the 2006–07 season, nearly 90,000 students on 8,846 teams  from around the world competed. The initial levels of competition are managed by a FIRST State Partner (such as NC FIRST). The Partner has complete control over all official tournaments in their region. Most Partners have a two-tier system; teams first go to a local tournament, and selected teams go on to states.
The largest single-day regional qualifying tournament is hosted by First State Robotics and First State FIRST Lego League in Wilmington, Delaware . Taking place every January, this event holds FIRST Lego League Jr. (FLL Jr.; grades K-3), FIRST LEGO League (FLL; grades 4–8), FIRST Tech Challenge (FTC; grades 9–12), FIRST Robotics Competition (FRC; grades 9–12), and robot sumo competitions under one roof at the University of Delaware's Bob Carpenter Center. Teams from Eastern Pennsylvania, Southern New Jersey, Delaware, and Maryland (among other regions) attend this tournament to make it the largest single-day FIRST event in the world. 
The only competition run by FIRST is the FIRST World Festival .  This is technically not an official level of competition because not all states may attend (there is a lottery system). In 2007, 96 teams competed in the FLL World Festival in Atlanta, Georgia on April 27–30.  The 2007–08 Power Puzzle FLL World Festival and the 2008–09 FLL World Festival on Climate Connections were held again in the Georgia Dome and Georgia World Congress Center . Starting with the 2010-11, FLL World Festival is held at the Edward Jones Dome and America's Center in St. Louis.
Additionally, the Champions Award winners from each state/provincial tournament may participate in one of the Open Championships which are organized by FLL Partners or a private invitational (such a Razorback University or Legoland CA).
As such, teams are normally allowed to win only one core (judged) award. Teams can win an additional award based on their robot's performance during the robot game competition portion of the tournament. 
The challenges for FLL are based on several different themes:
|Year||Theme||Number of participants ||Number of teams ||Notes|
|1999||First Contact ||9,500||975||It focused around a group of astronauts stranded in a space station; missions included pulling a lever to allow the astronauts into a chamber and delivering oxygen (foam balls) to different sections of the playing field.|
|2000||Volcanic Panic ||15,000||1,540||In this challenge, robots had to complete challenges prior to the eruption of a volcano,  such as rescuing a stranded scientist, barricading a village from lava rocks, deploying a gas sensor, and retrieving crates of samples, among other volcano-related tasks.|
|2001||Arctic Impact ||18,500||1,902||Robots had to complete tasks on an Arctic themed board such as retrieving medicine barrels, and rescuing minifigure scientists from polar bears.|
|2002||City Sights||27,009||3,001||Robots completed tasks such as clearing rocks off a soccer field, harvesting and delivering food loops, collecting toxic barrels, activating a windmill, and other city-related tasks. |
|2003||Mission Mars||42,000||4,331||Inspired by the year's Mars Rover mission , competing teams had to design and construct robots to solve a number of problems like removing rocks from a 'solar panel' to ensure a Mars base energy supply, collect 'soil/rock samples' from the Martian desert landscape, etc. |
|2004||No Limits||50,000||5,859||Centered around various robotic assistant systems for disabled persons, robots demonstrate how the systems are (hopefully) able to solve the given problems in a satisfying way. |
|2005||Ocean Odyssey||60,000||7,501||Involved marine-themed tasks such as mapping a sunken ship, deploying a research submarine, and cleaning up a shipping spill. |
|2006||Nano Quest||90,000||8,847||The challenge is developing anything using nanotechnology  that improves or makes life easier from medicine to computers to the environment. |
|2007||Power Puzzle||109,410||10,941||The challenge is on alternative energy and features tasks such as moving power lines, fuel sources and planting trees. |
|2008||Climate Connections||13,705||The challenge focuses on the Earth's past, present, and future climate. Students must research a climate problem occurring in their area, find a solution, then share it. They also have to research another area which has the same problem as their area. Featured moving balls, bicycles, computers, setting up levees, etc.  |
|2009||Smart Move ||14,725||The challenge centers around efficient transportation  and teams are to solve a particular problem with the mode of transportation that they have chosen. The robot game includes activating access markers, collecting loops, toggling a lever to move a truck, avoid warning beacons, parking at one of two specified locations, etc.|
|2010||Body Forward ||16,762||Explore the cutting-edge world of biomedical engineering to discover innovative ways to repair injuries, overcome genetic predispositions, and maximize the body's potential, with the intended purpose of leading happier and healthier lives. The robot game includes moving bionic eyes to the upper body, separating red and white blood cells, opening a door, and more.|
|2011||Food Factor||204,000 ||18,323||Improving the quality of food by finding ways to prevent food contamination.   The missions include removing bacteria, delivering food, and refrigeration.|
|2012||Senior Solutions||20,430 ||Improve and maintain the quality of life of senior citizens |
|2013||Nature's Fury ||"20,000+" ||Explore the awe-inspiring storms, quakes, waves and more that we call natural disasters. Teams will discover what can be done when intense natural events meet the places people live, work, and play.|
|2014||World Class - Learning Unleashed ||"25,000+" ||Redesign how we gather knowledge and skills in the 21st century. This includes learning any kind of skill at any age.|
|2015||Trash Trek ||"233,000+" ||"29,000+"||Find better ways to manage our trash.|
|2016||Animal Allies ||"28,000+"||The 2016 ANIMAL ALLIES season is all about our furry, feathered, and finned friends. What might become possible when we learn to help each other? |
The original robotics kit used by FLL was the RCX Mindstorms kit, which Lego no longer sells to the general public. In August 2006, LEGO released a new Mindstorms kit called the NXT . In 2006 and 2007, teams using the RCX could earn "fairness bonus" points based on the fact that the RCX was less technologically advanced.  However, the "fairness bonus" was discontinued for the 2008-09 season because tournament experience proved that the RCX teams were competitive and did not need it. In 2013, the NXT series kit was superseded by the EV3 series and the competition guidelines were updated to allow both EV3 and NXT-based robots to compete.
Global Innovation Award
Officially registered teams can also compete in the Global Innovation Award, where they could win a grant to make their project a reality. As of World Class, the First Place team wins $20,000 and the other two Finalists each win $5,000.  The money can be used to further the team's ideas or to continue in FIRST programs.  Every team member on a Finalist team also receives one LEGO Mindstorms EV3 Home Edition set.  The teams must submit their ideas using an online interface by completing a team summary (public), a idea summary (public), and 4 detailed idea analysis (private).  The questions have strict size limits (500-1000 chars). After the deadline, the submissions are reviewed by a panel of judges consisting of experts from engineering and industrial fields as well as experts in the challenge theme for that year. Teams are judged on problem identification, innovation, implementation, and effective use of STEM principles.  Twenty teams are selected to move on to the Semi-Finalist event at the FLL World Festival, where 3 Finalists are selected to move on to an event in Washington, D.C. At the D.C. event, the winner of the $20,000 award is announced.