As a member of the European Union and the Schengen travel zone, Germany welcomes other members’ citizens with their valid national identity cards (British citizens, having no national identity card, require a passport). 

United States, Canadian and Australian citizens need to present passports and can enter the country for 90 days (within a 180 day period) without applying for a visa. The 90 days includes time spent in other Schengen countries and the 180 day period starts from the first entry into a Schengen country. Anyone wishing to stay longer than 90 days (within a 180 day period) should contact their local German embassy for an extension visa before they go.

New Zealand citizens can spend up to 90 days without a visa in Germany, regardless of time already spent in other Schengen countries. For more information on this special visa exemption, visit the European Union website.

If you are arriving in Germany from another EU nation which is also a signatory of the Schengen Agreement, there is no border control. If you arrive by air from another Schengen Country, you may go through the BLUE EU gate and do not need to show identification or declare anything. Member states are: Germany, France, Belgium, Holland, Luxembourg, Denmark, Finland, Greece, Italy, Iceland,  Monaco, Norway, Sweden, Austria, San Marino, Spain, Vatican City, Portugal, Estonia, Latvia, Lithuania, Poland, Czech Republic, Slovakia, Slovenia, Switzerland, Hungary and Malta

NOTE  that the UK, Ireland, Liechtenstein, and Cyprus are Schengen signatories but have not yet joined the Agreement's "Open Borders" policy. You must go through customs if you arrive in Germany or any other Schengen country from one of these or any other nations worldwide.

Schengen Agreement Information (in German)