for a number of reasons

While often associated with happiness, dogs may wag their tails for a number of reasons.

when they are happy or excited

Dogs wag their tails when they are happy or excited.

happiness

Although there are many reasons why a dog wags a dog's tail, happiness is one of the most clear and known to us.

to show they're happy

“Experts” say: Dogs wag their tails back and forth to show they're happy.

excitement

On most breeds a wagging tail indicates excitement, usually of a good nature.

When a dog is happy

When a dog is happy, a dog wags a dog's tail.

when they are happy or excited to see their owners

Dogs wag their tails frequently when they are happy or excited to see their owners.

to the right to the left when confronted with something they want to back away from

I've raised this question whether dogs are conservative, because a reader named Alice sent me an article from the website of the magazine Nature that says this: 'Dogs wag their tails to the right when they see something they want to approach, and to the left when confronted with something they want to back away from.'

as a means of communication

Dogs wag their tails as a means of communication.

curiosity

Dogs chase their tails for a variety of reasons: curiosity, exercise, play, anxiety, predatory instinct or fleas.

to the right to the left when confronted with something they would rather avoid

– Mike found that dogs wag their tails to the right when they see something they want to approach, and to the left when confronted with something they would rather avoid.

due to excitement and happiness

Dogs wag their tail due to excitement and happiness.

an indication of joy or excitement

For years, folklore has relayed that a dog’s wagging tail is an indication of joy or excitement, whilst in cats cats can be a sign or wariness or distress - emotional states which any pet owner will attest to.

encouragement

Dogs wag their tails as a sign of friendly greeting or encouragement.

as a sign of excitement

Dogs wag their tails as a sign of excitement.

communication

A wagging tail is a form of dog communication.

in happiness

Some dogs wag their tails in happiness when they hear someone is at the door of the house.

anticipation of social interaction

“Dogs wag their tails as a sign of happiness and anticipation of social interaction.

If not just to indicate happiness

If not just to indicate happiness, then why do dogs wag their tails?

can mean many different things

A dog’s wagging tail can mean many different things; wagging tail is not always an expression of happiness.