Plastics are a wide range of synthetic or semisynthetic materials that use polymers as a main ingredient. Plasticity makes it possible for plastics to be molded, extruded, or pressed into solid objects of various shapes. This adaptability, combined with a wide range of other properties, such as lightweight, durability flexibility, nontoxicity, and lower costs to produce, led to their widespread use in various applications around the world. Most plastics derive from natural gas and petroleum, and a small fraction from renewable materials, with one such material being polylactic acid.

Between 1950 and 2017, 9.2 billion metric tons of plastics are estimated to have been made, with more than half of this amount being produced since 2004. In 2023 alone, preliminary figures indicate that over 400 million metric tons of plastic were produced worldwide. If global trends in plastic demand continue, it is projected that annual global plastic production will exceed 1.3 billion tons by 2060. The primary uses for plastic include packaging, which makes up about 40% of its usage, and building and construction, which makes up about 20% of its usage.

The success and dominance of plastics since the early 20th century has had major benefits for mankind, ranging from medical devices to light-weight construction materials. The sewage systems in many countries relies on the resiliency and adaptability of polyvinyl chloride (PVC). It is also true that plastics are the basis of widespread environmental concerns, due to their slow decomposition rate in natural ecosystems. Most plastics produced have not been reused. Some are in fact unsuitable for reuse. A sizeable amount of plastic wastes are directed to landfills adding to the already major and growing plastic pollution. Particular concern focuses on microplastics. Marine plastic pollution, for example, creates garbage patches. Of all the plastic discarded so far, some 14% has been incinerated and less than 10% has been recycled into less demanding applications.

In developed economies, about a third of plastics are used in packaging and roughly the same as buildings materials and products such as piping, plumbing or vinyl siding. Other uses include automobiles (up to 20% of plastics), furniture, and toys. In the developing world, the plastic uses may differ. For example, 42% of India's plastic consumption is used in packaging. Worldwide, about 50 kg of plastic is produced annually per person, with production doubling every ten years.

The world's first fully synthetic plastic was Bakelite, invented in New York in 1907, by Leo Baekeland, who coined the term "plastics". Dozens of different types of plastics are produced today, such as polyethylene, which is widely used in product packaging, and PVC, used in construction and pipes because of its strength and durability. Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger, who has been called "the father of polymer chemistry", and Herman Mark, known as "the father of polymer physics".

Most plastics contain organic polymers. The vast majority of these polymers are formed from chains of carbon atoms, with or without the attachment of oxygen, nitrogen or sulfur atoms. These chains comprise many repeating units formed from monomers. Each polymer chain consists of several thousand repeating units. The backbone is the part of the chain that is on the main path, linking together a large number of repeat units. To customize the properties of a plastic, different molecular groups called side chains hang from this backbone; they are usually attached to the monomers before the monomers themselves are linked together to form the polymer chain. The structure of these side chains influences the properties of the polymer. Thermoplastics do not undergo chemical change in their composition when heated and thus can be molded repeatedly.