The electronics industry emerged in the 20th century and is today one of the largest global industries. Contemporary society uses a vast array of electronic devices built in automated or semi-automated factories operated by the industry. Products are primarily assembled from metal-oxide-semiconductor (MOS) transistors and integrated circuits, the latter principally by photolithography and often on printed circuit boards. The size of the industry and the use of toxic materials, as well as the difficulty of recycling has led to a series of problems with electronic waste. International regulation and environmental legislation has been developed in an attempt to address the issues. The electronics industry consists of various sectors. The central driving force behind the entire electronics industry is the semiconductor industry sector, which has annual sales of over $481 billion as of 2018. The largest industry sector is e-commerce, which generated over $29 trillion in 2017. The most widely manufactured electronic device is the metal-oxide-semiconductor field-effect transistor (MOSFET), invented in 1959, which is the "workhorse" of the electronics industry.