Aachen is, with around 249,000 inhabitants, the 13th-largest city of North Rhine-Westphalia, and the 28th-largest city of Germany.

The city is the westernmost city in Germany and borders Belgium and the Netherlands to the west. It is located between Maastricht and Liège in the west, and Bonn and Cologne in the east. The city is flown through by the Wurm River, and together with Mönchengladbach, Aachen is the only larger German city in the drainage basin of the Meuse. Aachen is the seat of the City Region Aachen.

Aachen developed from a Roman settlement and spa, subsequently becoming the preferred medieval Imperial residence of Emperor Charlemagne of the Frankish Empire, and, from 936 to 1531, the place where 31 Holy Roman Emperors were crowned Kings of the Germans.

One of Germany's leading institutes of higher education in technology is located in the city. Its university hospital Uniklinik RWTH Aachen is Europe's largest single-building hospital. Aachen's industries include science, engineering and information technology. In 2009, Aachen was ranked eighth among cities in Germany for innovation.

The regional dialect spoken in the city is a Central Franconian, Ripuarian variant with strong South Low Franconian (Limburgish) influences from the dialects in the neighbouring Netherlands. As a Rhenish city, Aachen is one of the main centres of carnival celebrations in Germany, along with Cologne, Mainz and Düsseldorf. The culinary speciality the city is best known for are Aachener Printen, a type of gingerbread.

Aachen Cathedral was erected on the orders of Charlemagne. Construction began c. AD 796 and it was, on completion c. 798, the largest cathedral north of the Alps. It was modelled after the Basilica of San Vitale, in Ravenna, Italy, and was built by Odo of Metz. Charlemagne also desired for the chapel to compete with the Lateran Palace, both in quality and authority. It was originally built in the Carolingian style, including marble covered walls, and mosaic inlay on the dome. On his death, Charlemagne's remains were interred in the cathedral and can be seen there to this day. The cathedral was extended several times in later ages, turning it into a curious and unique mixture of building styles. The throne and gallery portion date from the Ottonian, with portions of the original opus sectile floor still visible. The 13th century saw gables being added to the roof, and after the fire of 1656, the dome was rebuilt. Finally, a choir was added around the start of the 15th century.

After Frederick Barbarossa canonised Charlemagne in 1165 the chapel became a destination for pilgrims. For 600 years, from 936 to 1531, Aachen Cathedral was the church of coronation for 30 German kings and 12 queens. The church built by Charlemagne is still the main attraction of the city. In addition to holding the remains of its founder, it became the burial place of his successor Otto III. In the upper chamber of the gallery, Charlemagne's marble throne is housed. Aachen Cathedral has been designated as a UNESCO World Heritage Site.

Most of the marble and columns used in the construction of the cathedral were brought from Rome and Ravenna, including the sarcophagus in which Charlemagne was eventually laid to rest. A bronze bear from Gaul was placed inside, along with an equestrian statue from Ravenna, believed to be Theodric, in contrast to a wolf and a statue of Marcus Aurelius in the Capitoline. Bronze pieces such as the doors and railings, some of which have survived to present day, were cast in a local foundry. Finally, there is uncertainty surrounding the bronze pine cone in the chapel, and where it was created. Wherever it was made, it was also a parallel to a piece in Rome, this in Old St. Peter's Basilica.

Aachen Cathedral Treasury has housed, throughout its history, a collection of liturgical objects. The origin of this church treasure is in dispute as some say Charlemagne himself endowed his chapel with the original collection, while the rest were collected over time. Others say all of the objects were collected over time, from such places as Jerusalem and Constantinople. The location of this treasury has moved over time and was unknown until the 15th century when it was located in the Matthiaskapelle (St. Matthew's Chapel) until 1873, when it was moved to the Karlskapelle (Charles' Chapel). From there it was moved to the Hungarian Chapel in 1881 and in 1931 to its present location next to the Allerseelenkapelle (Poor Souls' Chapel). Only six of the original Carolingian objects have remained, and of those only three are left in Aachen: the Aachen Gospels, a diptych of Christ, and an early Byzantine silk. The Coronation Gospels and a reliquary burse of St. Stephen were moved to Vienna in 1798 and the Talisman of Charlemagne was given as a gift in 1804 to Josephine Bonaparte and subsequently to Rheims Cathedral. 210 documented pieces have been added to the treasury since its inception, typically to receive in return legitimisation of linkage to the heritage of Charlemagne. The Lothar Cross, the Gospels of Otto III and multiple additional Byzantine silks were donated by Otto III. Part of the Pala d'Oro and a covering for the Aachen Gospels were made of gold donated by Henry II.[61] Frederick Barbarossa donated the candelabrum that adorns the dome and also once "crowned" the Shrine of Charlemagne, which was placed underneath in 1215. Charles IV donated a pair of reliquaries. Louis XI gave, in 1475, the crown of Margaret of York, and, in 1481, another arm reliquary of Charlemagne. Maximilian I and Charles V both gave numerous works of art by Hans von Reutlingen. Continuing the tradition, objects continued to be donated until the present, each indicative of the period of its gifting, with the last documented gift being a chalice from 1960 made by Ewald Mataré.

The Aachen Rathaus, (English: Aachen City Hall or Aachen Town Hall) dated from 1330, lies between two central squares, the Markt (marketplace) and the Katschhof (between city hall and cathedral). The coronation hall is on the first floor of the building. Inside one can find five frescoes by the Aachen artist Alfred Rethel which show legendary scenes from the life of Charlemagne, as well as Charlemagne's signature. Also, precious replicas of the Imperial Regalia are kept here.

Since 2009, the city hall has been a station on the Route Charlemagne, a tour programme by which historical sights of Aachen are presented to visitors. At the city hall, a museum exhibition explains the history and art of the building and gives a sense of the historical coronation banquets that took place there. A portrait of Napoleon from 1807 by Louis-André-Gabriel Bouchet and one of his wife Joséphine from 1805 by Robert Lefèvre are viewable as part of the tour.

As before, the city hall is the seat of the mayor of Aachen and of the city council, and annually the Charlemagne Prize is awarded there.

The Grashaus, a late medieval house at the Fischmarkt, is one of the oldest non-religious buildings in central Aachen. It hosted the city archive, and before that, the Grashaus was the city hall until the present building took over this function.

The Elisenbrunnen is one of the most famous sights of Aachen. It is a neo-classical hall covering one of the city's famous fountains. It is just a minute away from the cathedral. Just a few steps in a south-easterly direction lies the 19th-century theatre.

Also of note are two remaining city gates, the Ponttor (Pont gate), 800 metres (½ mile) northwest of the cathedral, and the Marschiertor (marching gate), close to the central railway station. There are also a few parts of both medieval city walls left, most of them integrated into more recent buildings, but some others still visible. There are even five towers left, some of which are used for housing.

St. Michael's Church was built as a church of the Aachen Jesuit Collegium in 1628. It is attributed to the Rhine mannerism, and a sample of a local Renaissance architecture. The rich façade remained unfinished until 1891, when the architect Peter Friedrich Peters added to it. The church is a Greek Orthodox church today, but the building is used also for concerts because of its good acoustics.

The synagogue in Aachen, which was destroyed on the Night of Broken Glass (Kristallnacht), 9 November 1938, was reinaugurated on 18 May 1995. One of the contributors to the reconstructions of the synagogue was Jürgen Linden, the Lord Mayor of Aachen from 1989 to 2009.

There are numerous other notable churches and monasteries, a few remarkable 17th and 18th-century buildings in the particular Baroque style typical of the region, a synagogue, a collection of statues and monuments, park areas, cemeteries, among others. Among the museums in the town are the Suermondt-Ludwig Museum, which has a fine sculpture collection and the Aachen Museum of the International Press, which is dedicated to newspapers from the 16th century to the present. The area's industrial history is reflected in dozens of 19th and early 20th-century manufacturing sites in the city.