What is the difference between a haiku and a limerick?

A haiku is a 3-line poem that does not rhyme. It is a Japanese form of poetry.
The first line has 5 syllables
The second line has 7 syllables
The third line has 5 syllables

Example:
The day is peaceful
The streets have no cars, but why?
A day of mourning

A limerick is a 5-line poem, it does rhyme, and is usually funny. It's origin has been debated about but it first appeared in a dictionary in the UK.

Type of Rhyme:
Lines 1, 2 and 5 rhyme
Lines 3, 4 rhyme

There is a certain Rhythm as well. if you want to write one, you need to know this. Read more about it here: http://www.poetry4kids.com/blog/lessons/how-to-write-a-limerick

Summary

A haiku is shorter than a limerick and does not rhyme.

A haiku has less rules and so is easier to write than a limerick.

A haiku is normally not funny, and a limerick is.

A limerick has more of a chance to make your laugh than a haiku.

A limerick sounds more like "real" poetry because it rhymes.

A limerick is longer than a haiku.