Although Danish and Norwegian are very similar languages, there are more differences between them than a cursory examination would lead one to believe.

German influence

First of all, Danish has adopted many German words and some grammatical influences not so frequently used in Norwegian. An example is names of countries. Danish generally uses the German names of countries, or at least the German ending; this means that the usual ending is -a in Norwegian and -en or -et in Danish. The Danish names are however often used in conservative Norwegian.

English:   Turkey 
Danish:    Tyrkiet 
Norwegian: Tyrkia

Differences in pronunciation

The difference in pronunciation between Norwegian and Danish is much more striking than the difference between Norwegian and Swedish. Danish speakers generally do not understand Norwegian very well, especially varieties other than Riksmål/Bokmål. Some Norwegians also have problems understanding Danish, but according to a recent scientific investigation they are better at understanding Danish than the Danes are at understanding Norwegian. [1]

The Danish pronunciation is softer and the letters d, r and g in particular are pronounced quite differently. (For example, the Danish g is pronounced as y or ou in Norwegian.

Grammatical differences

Prepositions

The main difference in use of prepositions in the Danish and Norwegian language is the use of i/på, (in English in/on. In many cases the rules are the same, but there are still many exceptions. For example if you were to say I'm going out (as in out to a bar or a disco) you would say in Norwegian Jeg går på byen (literally I go on the city) but in Danish you would say Jeg går i byen (literally I go in the city – in Norwegian, this sentence would mean I walk in the city).

Another difference is the use of the definite endings. In Danish, the definite ending is used similarly to the definite article in English, so that I love that man becomes Jeg elsker den mand. In Norwegian, the definite article is still used even if a specific example is already indicated with den (that): I love that man becomes Jeg elsker den mannen in Norwegian, literally I love that the man.