Haiger (German pronunciation: [ˈhaɪɡɐ] ^ⓘ) is a country town in the Lahn-Dill-Kreis in Hesse, Germany. The nearest city is Siegen, about 25 km north of Haiger.

Haiger lies about 5 km west of Dillenburg, and 20 km southeast of Siegen on the eastern edge of the Westerwald range, near where the three states of Hesse, North Rhine-Westphalia and Rhineland-Palatinate all share a common point. It is the district's northernmost town. The river Dill rises north of the constituent community of Offdilln.

Haiger borders to the north the town of Netphen (Siegen-Wittgenstein in North Rhine-Westphalia) and the community of Dietzhölztal, to the east with the community of Eschenburg and the town of Dillenburg, to the south with the community of Breitscheid (all in the Lahn-Dill-Kreis), and to the west with the communities of Burbach and Wilnsdorf (both in the Siegen-Wittgenstein district of North Rhine-Westphalia).

Following a local government reform in the 1970s the rural villages of Sechshelden, Langenaubach, Flammersbach, Allendorf, Kalteiche, Haigerseelbach, Steinbach, Rodenbach, Fellerdilln, Dillbrecht, Offdilln, Weidelbach, Oberroßbach and Niederroßbach became part of the district of Haiger. These are culturally diverse and speak different versions of the local dialect. ^{[citation needed]}

(in each case on 31 December)

Haiger is the earliest documented town on the river Dill. It was first mentioned in 778 in a gift deed of Lorsch monastery. The town is located at the meeting of three small valleys formed by the Haigerbach, Aubach and Dill, which in medieval times placed the town along important communication routes, but later more on the periphery. The town's most famous son was Johann Textor who was born here in 1582. Between 1608 and 1619 he was town clerk in Haiger and subsequently wrote the Nassauische Chronik, a comprehensive description of the area. One of the most famous historic depictions of the town is an engraving by Matthäus Merian. On 8 May 1729, the still fully walled town perished in a great fire that destroyed all buildings within a few hours. Even the town's church, built on an outcrop rising within the centre of town, was left in ruins. Quick financial help from surrounding principalities, towns and provinces, as well as a generous donation of 400 florins by Princess Isabella of Nassau-Dillenburg, helped relieve some of the worst deprivation.

The nobles of Haiger were influential in the Haigermark. The Haigermark was also known as the Land of the Free Men (predium liberorum virorum), likely owing to the Knights' free rule (without intervening overlords between the family and the emperor). The family's influence gradually waned with the rise of the house of Nassau-Dillenburg.

The town's name, Haiger, is possibly derived from old middle German. The great number of herons (German: Fischreiher) on the Haigerbach, Aubach and Dill may have helped to give the town the name Reiherbach, or in old middle German Heigerahe. This name came from the words Heiger ( = Reiher) and Ahe ( = Bach; brook or waterway). Over the centuries, the spelling changed many times: → "Heigrahe" → "Heigera" → "Heigere" → "Heigerin" → "Heigre" → "Heigeren" → "Hegere" → "Hegera" → "Heygere" → "Heyger" → "Heiger" → "Häger" → "Häyer". Eventually, this became Haiger. The bird in the coat of arms may likewise be a reference to the herons, although it might also be a corruption of what was once the Lion of Nassau (see Coat of arms below).