Hamburg would be nothing without its harbour. The shipping business has been very influential on the development of the city, and still is the most important activity in town. And it's still booming - in 2006, Hamburg's harbour had 134.900 tonnes of cargo turnover, more than double the amount of 1991. The switch that was made to container shipping in recent decades has proved essential, as now 97% of all cargo passing through Hamburg is in containers, compared to 68% in 1990. Hamburg had only 200 residents when the harbour was first mentioned indocuments in the 9th century. The town got market rights in 937, marking the start of Hamburg's economic progress. The port is considered to have started in 1189, when Emperor Frederick Barbarossa's charter officially granted the town market rights and customs-free travel along the Elbe to the sea. Hamburg joined the medieval trade association of the Hanseatic League in 1321, and became an important link between cities on the Baltic coast and those along the North Sea. Trading expanded to include Scandinavia, Bruges, London and Amsterdam. At that time, trade ships were guarded from pirates, (like the infamous Klaus Störtebecker) by convoy fleets supplied by
the city.
The League proved very successful and Hamburg quickly grew to 16000 residents in 1450. Trade patterns shifted as the Baltic trade became less important, and the discovery of the Americas lead to new products and trading routes. The 18th century saw the start of trade with America. Hamburg's trading fleet went from 150 ships in 1788 to 280 in 1799, and steamships were introduced from 1816, greatly increasing the ships' reliability and speed.
The harbour was expanded and modernised in the late 1800s, when new docks further away from the city centre were made. At the same time, the famous city-centre Speicherstadt warehouses were built, a massive undertaking resulting in the world's largest single warehouse complex, even today.
Hamburg joined in Bismarck's drive for German unity, leaving just the harbour area as a customs enclave for another 114 years. The city kept modernising with new jetties at St. Pauli and the 1911 Elbe Tunnel, and by 1913 Hamburg had a million inhabitants and was the third largest harbour after London and New York. In the Second World War 80% of the  harbour facilities were destroyed, but rapid reconstruction ensured the harbour was back on track by 1955. 
Modernisation was the keyword, and investments in container facilitiespaid off handsomely. The HafenCity urban planning project is the latest project to transform the harbour city; it is set to transform 160 hectares between Kehrwiederspitze and the Elbe bridges, and plans include apartments, offices, recreational facilities and a new cruiseliner terminal. For more information about the harbour, see www.hafen-hamburg.de.

Harbour sights
Although much of the harbour is off-limits to casual visitors, it's possible to see plenty shipping-related activities on short trips in and from the city centre. On dry land, the Speicherstadt is a great place to wander and learn about the importance of warehouses for the city's economy. To see the city from the water, visitors can also join one of many Alster Steamer boat trips through the canals and harbours, or a trip that explores the modern harbour, passing massive container ships.

Museum ships
Two museum ships moored in central Hamburg merit a visit:

Cap San Diego - Moored at the Überseebrücke quay, the Hamburg-built Cap San Diego freight ship from 1961 is the world's largest functional cargo museum ship, doing regular day trips with passengers on board and even offering accommodation. You can tour the ship, visiting the cargo holds, loading gear, mooring and anchoring equipment, palaver deck, lifeboats, swimming pool and several other rooms. She's 160m long with a loading capacity of 10,300 tons, and completed over 120 trips to South America before becoming obsolete by the containerisation of cargo shipping.
Cap San Diego, Überseebrücke quay, www.capsandiego.de. Open 10:00-18:00. Admission €6/2.50. Rooms: passenger cabins singles €72,doubles €90; captain’s cabin €125.

Rickmer Rickmers - The elegant Rickmer Rickmers three-master museum ship, moored at the Landungsbrücken, is one of the last cargo sailing ships. Made with steel in 1896, the 97m-long ship used 24 sails and was used for trips to East Asia and in Europe before finally saved from being scrapped in 1974. Visitors can tour the ships holds and crew rooms and learn more about life on the high seas. 
Landungsbrücken, Ponton 1a, www.rickmer-rickmers.info. Admission €3/2. Open 10:00-18:00.