Elle se compose de briques emboîtables, de figurines et diverses autres pièces. Les briques Lego peuvent être assemblées et reliées afin de construire des objets tels que des véhicules, des bâtiments, des robots. Les constructions peuvent être démontées pour créer de nouveaux montages avec les pièces. The Lego Group a commencé à fabriquer des briques de jeu à verrouillage en 1949.

Les briques Lego constituent un ensemble d’éléments modulaires. De ce fait, leurs dimensions sont multiples d’une valeur de base, appelée module et constituant l’unité Lego, et qui vaut en l’occurrence 1/8 de pouce (soit 3,175 mm).

Si on considère la brique la plus commune, de 2×4 plots, elle est large de 5/8 de pouce (15,875 mm), longue de 10/8 (31,75 mm) et haute de 3/8 (plots non inclus), soit trois fois la hauteur d’une plaque. Un plot a pour rayon 2,38125 mm, de plus, l’espace entre deux plots vaut 1/8 de pouce, ce qui permet d’y glisser une plaque. Ainsi en superposant 4 plaques 2×2 et une tuile, on obtient un cube de 5/8 de côté. La plupart des produits concurrents sont proposés dans les mêmes dimensions, une compatibilité qui les rend plus attrayants pour le consommateur.

Les premières briques, en 1949, étaient relativement simples : une coque vide avec des plots sur le dessus. Deux fentes latérales conféraient aux briques l’élasticité suffisante pour l’assemblage. Le brevet du 28 janvier 1958 concerne le modèle actuel, avec en particulier les fûts cylindriques disposés à l’intérieur de la coque venant en quinconce avec les plots : ainsi, le nombre de contacts entre deux éléments superposés est augmenté et garantit la bonne tenue des briques. Plus tard, pour les briques d’au moins 2×2, l’épaisseur de la coque est diminuée, et compensée par de petites nervures. Enfin, une nervure centrale assure la bonne tenue des parois et limite le retrait au moulage.

À la simplicité d’utilisation correspondent une recherche et une précision dans la fabrication. Les briques sont testées aux différents stades de leur production ; elles sont produites avec un précision de 10 μm1. En 2008, le nombre de pièces défectueuses était estimé à une vingtaine de briques par million.

Un des éléments-clés fut d’être un système complet. Chaque nouvelle série ou ensemble est compatible avec le reste du système : quelles que soient ses dimensions, sa forme ou sa fonction, chaque pièce est utilisable avec toutes les autres. L’engrenage et les mécanismes motorisés inclus dans les modules techniques les plus avancés peuvent être attachés presque sans effort aux Duplo pour les enfants de trois ans. Ces possibilités infinies arrivent même à fasciner les adultes.

Avec la composition précise de l’ABS, les moules sont la pierre angulaire du succès commercial de Lego. Ces moules sont donc des pièces à (très) haute valeur stratégique pour Lego. Lorsqu’un moule n’est plus tout à fait conforme aux normes de qualité que s’impose son fabricant, il est coulé dans le béton d’un nouveau bâtiment Lego sur un site de l’entreprise.

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Lego is a popular line of construction toys manufactured by The Lego Group, a privately held company based in Billund, Denmark. The company's flagship product, Lego, consists of colourful interlocking plastic bricks and an accompanying array of gears, minifigures and various other parts. Lego bricks can be assembled and connected in many ways, to construct such objects as vehicles, buildings, and even working robots. Anything constructed can then be taken apart again, and the pieces used to make other objects. Lego began manufacturing interlocking toy bricks in 1949. Since then a global Lego subculture has developed, supporting movies, games, competitions, and six themed amusement parks.

History
1890s–1950s
The Lego Group began in the workshop of Ole Kirk Christiansen (born 7 April 1891), a carpenter from Billund, Denmark, who began making wooden toys in 1932. In 1934, his company came to be called "Lego", from the Danish phrase leg godt, which means "play well".

It expanded to producing plastic toys in 1947. In 1949 Lego began producing, among other new products, an early version of the now famous interlocking bricks, calling them "Automatic Binding Bricks". These bricks were based in part on the Kiddicraft Self-Locking Bricks, which were patented in the United Kingdom in 1939 and then there released in 1947. Lego modified the design of the Kiddicraft brick after examining a sample given to it by the British supplier of an injection-molding machine that the company had purchased. The bricks, originally manufactured from cellulose acetate, were a development of traditional stackable wooden blocks that locked together by means of several round studs on top and a hollow rectangular bottom. The blocks snapped together, but not so tightly that they required extraordinary effort to be separated.

The Lego Group's motto is det bedste er ikke for godt which means roughly "only the best is the best" (more literally "the best is never too good"). This motto was created by Ole Kirk to encourage his employees never to skimp on quality, a value he believed in strongly. The motto is still used within the company today. By 1951 plastic toys accounted for half of the Lego Company’s output, although Danish trade magazine Legetøjs-Tidende ("Toy-Times"), visiting the Lego factory in Billund in the early 1950s, felt that plastic would never be able to replace traditional wooden toys. Although a common sentiment, Lego toys seem to have become a significant exception to the dislike of plastic in children's toys, due in part to the high standards set by Ole Kirk.

Design
Lego pieces of all varieties constitute a universal system. Despite variation in the design and purpose of individual pieces over the years, each remains compatible in some way with existing pieces. Lego bricks from 1958 still interlock with those made in the current time, and Lego sets for young children are compatible with those made for teenagers. Each Lego piece must be manufactured to an exacting degree of precision. When two pieces are engaged they must fit firmly, yet be easily disassembled. The machines that make Lego bricks have tolerances as small as 10 micrometres. Primary concept and development work takes place at the Billund headquarters, where the company employs approximately 120 designers. The company also has smaller design offices in the UK, Spain, Germany, and Japan, which are tasked with developing products aimed specifically at these markets. The average development period for a new product is around twelve months, in three stages. The first stage is to identify market trends and developments, including contact by the designers directly with the market; some are stationed in toy shops close to holiday periods, while others interview children. The second stage is the design and development of the product based upon the results of the first stage. As of September 2008 the design teams use 3D modelling software to generate CAD drawings from initial design sketches. The designs are then prototyped using an in-house stereolithography machine. These are presented to the entire project team for comment and for testing by parents and children during the "validation" process. Designs may then be altered in accordance with the results from the focus groups. Virtual models of completed Lego products are built concurrently with the writing of the user instructions. Completed CAD models are also used in the wider organisation, such as for marketing and packaging.

Manufacture
Since 1963, Lego pieces have been manufactured from a strong, resilient plastic known as acrylonitrile butadiene styrene (ABS). As of September 2008, the engineers use the NX CAD/CAM/CAE PLM software suite to model the elements. The software allows the parts to be optimised by way of mould flow and stress analysis. Prototype moulds are sometimes built before the design is committed to mass production. The ABS plastic is heated to 232 °C (450 °F) until at a dough-like consistency. It is then injected into the moulds at pressures between 25 and 150 tons, and takes approximately 15 seconds to cool. The moulds are permitted a tolerance of up to two micrometres, to ensure the bricks remain connected. Human inspectors check the output of the moulds, to eliminate significant variations in colour or thickness. According to the Lego Group, about eighteen bricks out of every million fail to meet the standard required. Lego factories recycle all but about 1 percent of their plastic waste from the manufacturing process every year. If the plastic cannot be re-used in Lego bricks, it is processed and sold on to industries that can make use of it. Manufacturing of Lego bricks occurs at a number of locations around the world. Moulding is done in Billund, Denmark; Nyíregyháza, Hungary; and Monterrey, Mexico. Brick decorations and packaging is done at plants in Denmark, Hungary, Mexico and Kladno in the Czech Republic. The Lego Group estimates that in the course of five decades it has produced some 400 billion Lego blocks. Annual production of Lego bricks averages approximately 36 billion per year, or about 1140 elements per second. If all the Lego bricks ever produced were to be divided equally among a world population of six billion, each person would have 62 Lego bricks. According to an article in BusinessWeek in 2006, Lego could be considered the world's No. 1 tire manufacturer; the factory produces about 306 million tiny rubber tires a year. In December 2012, the BBC's More or Less programme asked the Open University's engineering department to determine "how many Lego bricks, stacked one on top of the other, it would take to destroy the bottom brick?" Using a hydraulic testing machine, the engineering department determined the average maximum force a 2×2 Lego brick can stand is 4,240 newtons; since an average 2×2 Lego brick has a mass of 1.152 grams (0.0406 oz), according to their calculations it would take a stack of 375,000 bricks to cause the bottom brick to collapse, which represents a stack 3,591 metres (11,781 ft) in height.