All vipers are venomous.

Vipers belong to the family Viperidae - one of four families that include venomous snakes. The viper family includes the adder, asp, mamba, the coral snake and moccasins. This family also has a sub group known as pit vipers (Crotalinae). They have special heat sensing pit organs between the nostril and the eye. The pit viper family includes the copperhead, rattlesnake, water moccasin and the bushmaster.

Another family is the Elapidae which includes cobras and kraits. The family Hydrophiidae includes the sea snake. The family Colubridae is a large family with mostly non-venomous snakes. The African boomslang and the African vine snake are both venomous but belong in this family.

Australia has the largest number of species of poisonous snakes in the world. In fact all of the top ten most deadly snakes in the world can be found there.

The top ten list includes:

10 - Western Brown Snake 
9 - Death Adder
8 - Black Tiger Snake
7 - Tiger Snake
6 - Sea Kraits
5/4 - Mainland and Eastern Tiger Snakes (it was a tie)
3 - Taipan
2 - King Brown Snake
1 - Inland Taipan

Rattlesnake skull showing the long deadly fangs.

Specific types of venom:

Neurotoxins - toxins that cause paralysis or interfere with nervous system function

Mytoxins - toxins that damage muscle

Haemotoxins - toxins that affect blood clotting

Haemorrhagins - toxins that damage blood vessels and cause bleeding

Haemolysins - toxins that damage red blood cells

Nephrotoxins - toxins that damage the kidney

Cardiotoxins - toxins that affect the heart

Necrotoxins - toxins that cause tissue death

Snake venom will usually be a neurotoxin, a haemotoxin or a cardiotoxin, in some cases, venom will have a combination of these toxins.