I happened upon an invitation to this puzzle recently, and I had already done it. So now I'll post it!

Out Of The Gate

We know that the Norwegian lives in the first house from clue 10. We also know that the Norwegian lives next to the blue house from clue 14. For the moment, we will assume that when clue 4 states that "The green house is on the left of the white house" it means immediately to the left. This means that the fifth house cannot be green. The first house also cannot be green, because the blue house is immediately to the right. The third house cannot be green because clue 8 tells us that the owner of the third house drinks milk, and clue 5 tells us that the owner of the green house drinks coffee. Hence, the fourth house is green and the fifth house is white.

Additionally, clue 1 tells us that the Brit is in the red house. The red house must be either the first or third, but the Norwegian already owns the first house. Hence, the Brit is in the third house, which is red. The Norwegian's house is yellow. Clue 7 states that the owner of the yellow house smokes Dunhills. Clue 11 states that the owner of horses is one house away from the man who smokes Dunhills, indicating that horses are in the second house.

We now have the following table

Trait	House 1	House 2	House 3	House 4	House 5
Nationality	Norwegian	?	Brit	?	?
House Color	Yellow	Blue	Red	Green	White
Drink	?	?	Milk	Coffee	?
Cigar	Dunhills	?	?	?	?
Pet	?	Horse	?	?	?

Picking Through The Field

The Dane must be in the second or fifth house since clue 3 states he drinks tea. The Swede has a dog, so he must own house 4 or 5. The framing of the problem states that there is only one correct answer, so let's put the Dane in 2, the German in 4, and the Swede in 5. If there is a contradiction, we can return here to resume our reasoning.

Clue 2 puts the dog in house 5. Clue 13 puts this Princes in house 4. We now have the following table.

Trait	House 1	House 2	House 3	House 4	House 5
Nationality	Norwegian	Dane	Brit	German	Swede
House Color	Yellow	Blue	Red	Green	White
Drink	?	Tea	Milk	Coffee	?
Cigar	Dunhills	?	?	Princes	?
Pet	?	Horse	?	?	Dog

Smoking!

According to clue 15, the smoker of Blends must neighbor the drinker of water. Hence, water cannot be house 5, since Blends is not house 4. Additionally, Blends cannot be house 5, since house 4 drinks coffee. Blends cannot be house 3 because it neighbors tea on the left and coffee on the right. We know that Blends are smoked in house 2 and water drunk in house 1. Beer is the only beverage left for house 5, meaning Bluemasters are smoked there (clue 12) leaving Pall Malls for house 3.

Trait	House 1	House 2	House 3	House 4	House 5
Nationality	Norwegian	Dane	Brit	German	Swede
House Color	Yellow	Blue	Red	Green	White
Drink	Water	Tea	Milk	Coffee	Beer
Cigar	Dunhills	Blends	Pall Mall	Princes	Bluemasters
Pet	?	Horse	?	?	Dog

The finish line

Clue 6 puts birds in house 3, and Clue 9 states that the Blends smoker is adjacent to the cat owner, meaning the Cats must be in house 1. That means that the fish belongs in house 4.

Taking this solution and verifying it against the rule list, we find no contridictions. Since we are told the solution is unique, we know that the fish belongs to the German in the green house, fourth down, who drinks coffee and smokes Princes.

Trait	House 1	House 2	House 3	House 4	House 5
Nationality	Norwegian	Dane	Brit	German	Swede
House Color	Yellow	Blue	Red	Green	White
Drink	Water	Tea	Milk	Coffee	Beer
Cigar	Dunhills	Blends	Pall Mall	Princes	Bluemasters
Pet	Cat	Horse	Bird	Fish	Dog