Conium maculatum, commonly known as hemlock (British English) or poison hemlock (in North America), is a highly poisonous flowering plant in the carrot family Apiaceae.

The plant is herbaceous, with no woody parts, and has a biennial lifecycle. Under the right conditions, the plant grows quite rapidly during the growing season and can reach heights of 2.4 metres (8 feet) with a long penetrating root. The plant has a distinctive odour that is usually considered unpleasant and carries with the wind. The hollow stems are usually spotted dark maroon and turn dry and brown after the plant completes its biennial lifecycle.

Native to Europe and North Africa, hemlock is a hardy plant that can live in a variety of environments. It is widely naturalised outside its native range, including in Australia, West Asia, and North and South America, where it can become an invasive weed.

All parts of the plant are toxic, particularly the seeds and roots, and especially when ingested. Hemlock is well-known as the poison that killed the philosopher Socrates after his trial in Ancient Greece.

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