Denizli is an industrial city in the southwestern part of Turkey and the eastern end of the alluvial valley formed by the river Büyük Menderes, where the plain reaches an elevation of about three hundred and fifty metres (1,148 ft). Denizli is located in the country's Aegean Region.

The city has a population of about 646,278 (2018 census). This is a jump from 389,000 in 2007, due to the merger of 13 municipalities and 10 villages when the area under Denizli Municipality jurisdiction increased almost fivefold and the population around 50 percent. Denizli (Municipality) is the capital city of Denizli Province.

Denizli has seen economic development in the last few decades, mostly due to textile production and exports.

Denizli also attracts visitors to the nearby mineral-coated hillside hot spring of Pamukkale, and with red color thermal water spa hotels Karahayit, just 5 kilometres (3 miles) north of Pamukkale. Recently, Denizli became a major domestic tourism destination due to the various types of thermal waters in Sarayköy, Central/Denizli (where Karahayit and Pamukkale towns are located), Akköy (Gölemezli), Buldan (Yenicekent), and Çardak districts.

The ancient ruined city of Hierapolis, as well as ruins of the city of Laodicea on the Lycus, the ancient metropolis of Phrygia. Also in the depending of Honaz, about 10 mi (16 km) west of Denizli is, what was, in the 1st century AD, the city of Colossae.

The weather is hot in Denizli in summers, whereas in winters, it may occasionally be very cold with snow on the mountains that surround the city. Some years, snow can be observed in the urban areas. Springs and autumns are rainy, mild climate, warm.